Unless you need a specific shape for a too-small-for-standard-kegs fridge, just buy used. As was said, the kegs are likely not the most expensive part of the kegging process.
Adventures in homebrewing currently has a sale on kegs:
4x pin lock for $149
4x ball lock for $199
http://www.homebrewing.org/Sale-Items_c_21.html
Personally I like the pin locks, aside from the price, because I can visually see they are locked (not that I've ever had a ball lock connection - beer or otherwise - fail me in any way).
*No connection to Adventures in Homebrewing, although they are my LHBS.