That is a pretty tight budget, I would go with this processor and RAM to leave some cash for a motherboard.
AMD Athlon 64 3200+: $75.00
http://www.newegg.com/Product/Produc...82E16819103535
Kingston ValueRAM 512MB (2x256MB): $54.49
http://www.newegg.com/Product/Produc...82E16820141433
Total comes to $130 with cash left over for a motherboard. Or maybe even a better processor.