fix a computer

Possible! If not included software, eg. Windows, MS office, etc..

CPU: AMD Athlon64 X2 5000+ ($475)
Mother board: ASUS M2A-VM HMDI ($600)
RAM: Corsair DDR2-800 1G x 2 ($380)
Display card: onboard Xpress X1250
Hard disc: Seagate ST3250410AS 120GB ($325)
DVD Re-writer: Liteon or LG ($200)
Case & transformer: seems to you ($500)

Total: $2480 (The price is quoted from internal, so, the actual price in the market will be less than this)

Possible.
Even a laptop computer.
See OLPC