Price typically depends on tensile strength, length and quantity. To get small 4 inch ones that can hold 18 pounds, you can pay
$1.25 for 100 pieces. That's a little more than 1 penny a piece. (Any color, doesn't really matter). Perfect for managing wires inside the desktop case.
If you want the bad boys that can hold 250 pounds than expect to pay more. To buy 25 of these 22 inch plastic ties will cost you about $9 over
here. Of course, these are good if you want you computer to be suspended from a cable OR for the chair you sit on.... etc... Actually can't think of anything I would do that would need a zip tie that big.