I'm sure you can find a quailty 21" inch moniter for less than $700 that's with warranty aswell.
As far as ordering a moniter from an online vendor it depends who you are dealing with, also keep in mind how far the item has to be shipped in order to get to you. So in the best possible circumstances you'd want to buy the moniter from instate or border states. The moniter will not only arrive quicker but will go through less transfer points and less people will touch it. I suggest 2nd AIR on expensive fragile components like a 21" inch moniter.
Always make sure you know who you are dealing with online, That cannot be stressed enough, A smart buyer won't get ripped. Make sure the moniter comes with a warranty, usually the supplier will accomadate you with a 1-3 year vendor warranty for extra charge but I usually just rely on the Manufacturers warranty (usually 3 years parts and labor or full replacment).
Anyhow if you are looking for a moniter I strongly suggest trying to find one locally, perhaps you have a Fry's or CompUSA or Circuit City store near by. If you can't find a moniter locally then price match and look for the best deal on sites like
www.pricegrabber.com and
www.pricewatch.com , they will likely find you the best deal for repetuable companies. Ebay and other auction sites are another option and sometiems you can find amazing deals on brand new boxed moniters for extremely cheap prices. I have a 21" inch Nokia moniter with a 3 year warranty and I got it for $550 U.S. , I could not be any happier.