I bought HP21 cartridge few months back for 23 dollars. Most of the generic ones are around 18. So I think, its a good price, if you only want a black one ( I only print black, sale is mostly on the combo ones or XL ).
If you bought a new printer ( listed below), then you can get it too, as the one coming with new printers are too small and goes out after 25-35 pages.
Secondly, many online stores to sell around this price, but shipping is a bugger.
Printers:
HP Deskjet 3920, Deskjet 3940, Deskjet D1360, Deskjet D1460, Deskjet D2360, Deskjet D2460, Deskjet F2100, Deskjet F2179, Deskjet F2180, Deskjet F2235, Deskjet F2275, Deskjet F2280, Deskjet F370, Deskjet F380, Deskjet F4185, Officejet 4355, PSC 1402, PSC 1410
Sweet, thanks :) - needed a 21 cartridge