I am not sure where you live, or if you are comfortable with buying things off of Craigslist...

1) You should be able to find a perfectly capable used iMac or macbook (pro) on Craigslist for anywhere between $400 - $800.

2) If Craigslist is not your thing, Apple has an excellent refurbished program, I have bought refurb. a number of times with no problems.

http://store.apple.com/us/browse/home/specialdeals/mac?mco=O...

3) If you want to go brand new, any of the MacBook Air's or iMac desktops would be perfect.