As a commercial lawyer, I thought I would add my $0.02. The below is provided for informational purposes only and does not in any way constitute a legal opinion relevant to the claims or potential claims of those reading this.
First, the basics: Any binding contract requires proof of offer and acceptance (together indicating mutual assent to the terms) and must be supported by consideration. Consideration is really anything of value that provides support for the idea that the parties truly intended to be bound to their respective ends of the bargain. Consideration need not be tangible or physical (e.g. actual transmission of money); a promise to do something beyond which you already have an obligation to do (or not to do) will suffice. For example, the promise to pay money in exchange for the promise to perform a service is adequate consideration to support the deal when you hire someone to paint your house. On the other hand, the promise to pay someone in exchange for their promise not to punch you in the nose is unenforceable since no one has the right to assault another person.
The Uniform Commercial Code (UCC) consists of model legal terms intended to govern, among other things, the sale of goods. Nearly every state has adopted the UCC into its body of law in one form or another. While the UCC provides some nice standardization in terms of how the law is worded, it does not really diverge from the basic law of contract mentioned above (i.e. offer, acceptance, consideration). Some states have decided the UCC provisions on sales do not apply to consumers, some say it does. In any event, its terms are likely useful to point out what is considered reasonable conduct when engaged in the sale of goods, regardless of who the purchaser is. A good example of this is Section 2-204 of the UCC which states that "A contract for sale of goods may be made in any manner sufficient to show agreement, including conduct by both parties which recognizes the existence of such a contract."
With respect to any on-line seller, one has to analyze whether the website extends an offer to sell or, rather, invites an offer to purchase, at the stated price. Generally, advertising (newspapers, catalogs, etc.) has been determined to be an invitation for customers to make an offer to purchase rather than an offer to sell. Similar logic would lead one to reasonably conclude that internet advertising on ones website should be treated similarly. Consequently, when we act to purchase from an on-line seller, we are the ones extending the offer to buy and it is the seller who must determine whether they will accept on those terms. Of course, most of the guesswork is removed from this process since the posted pricing would appear to indicate the price the seller will accept and the payment terms are usually obvious. Moving forward, let us assume that every card "purchaser" was actually an offeror-- extending an offer to BestBuy to buy the card for the stated price in the form of a credit card payment.
The next question would be whether BestBuy accepted the offer. UCC 2-206 (again, not inconsistent with basic contract law) provides the guidance that "an order or other offer to buy goods for prompt or current shipment shall be construed as inviting acceptance either by a prompt promise to ship or by the prompt or current shipment of conforming . . . goods. . . ." The main issue being whether the behavior of the accepting party is sufficiently particular to indicate assent to the deal. As for myself, I did not receive an immediate email confirming my order, but the BestBuy website did present order status information indicating my order was received and the goods were "on order." Is this enough to show acceptance of an order? Maybe. Some of us received "Backorder" notices indicating BestBuy "hope[ed] to be able to ship this item . . . soon." This would appear to add some weight to the argument that BestBuy is confirming its intent to sell the item for the stated price. I would also find it compelling if one could prove that the administrative portion of the credit card processing had also occurred (i.e. the charge amount is reserved against your spending balance). My own order was placed with an AMEX card, and I could not find any evidence of this having occurred-- at least via on-line access to my account. If this could be shown, I would think think all three of these factors are compelling evidence of assent to sell the card for the stated price (i.e. acceptance of our offers to purchase). The credit card information would probably be attainable via written request relative to your account-- small claims courts usually will issue subpoenas.
The last portion of the analysis (for me, anyway) is where BestBuy's terms and disclaimers enter the picture. The simplest point to make here is the obviousness with which the terms are accessible and displayed. I find it problematic that the terms are linked (thus not displayed through the ordinary purchase process) and that the link appears in relatively small type at the bottom of a webpage that is more than twice the size of a brower window. It is entirely conceivable that one could proceed to the checkout without ever seeing the link. Nor is there any statement during checkout that the order is being submitted or accepted subject to those terms. Disclaimers and conditions in the course of consumer transactions are usually viewed through a prism of the "least sophisticated purchaser," thus these factors would weigh in favor of a court not applying the terms.
Keep in mind that I am assuming acceptance can be established. An seller would be entitled to change prices (i.e. the amount for which it is soliciting offers) prior to it accepting an offer to purchase at that price. If the offer of $129.99 has, in fact, been accepted, I believe the above points would argue in favor of a court not allowing BestBuy to claim it reserved some right to rescind its acceptance of the offer. UCC 2-207 also supports this concept in that it provides that "A definite and seasonable expression of acceptance or a written confirmation which is sent within a reasonable time operates as an acceptance even though it states terms additional to or different from those offered or agreed upon, unless aceptance is expressly made conditional on assent to the additional or different terms." Without a clear and obvious statement to the effect that an acceptance is conditioned upon certain other terms, the acceptance to the offer stands.
I do not believe a claim such as these to be a "slam dunk," but I certainly believe that there is a real good possibility that BestBuy could lose a claim such as this. Damages would likely be computed as the difference between the price of the card elsewhere versus the BestBuy advertised price, about $300.00. Many states have consumer protection laws that, when invoked, allow recovery of up to triple the amount of actual damages in the event of deceptive trade practices-- YMMV. Note that many states allow appeals from small claims decisions in the form of re-trial in the larger court. While this necessarily adds time and expense, it also dissuades do-it-yourselfers from going to the next level because the procedures are much more technical and detailed and ripe for missteps by non-lawyers.