a config i made for a few people on a gaming budget of around $300 is
sempron 2400+ and mobo combo for $65 at outpost
512 pc 3200 $40
80gb sata $65
cheap case $30
radeon 9550 $65
optical drive $25
you could always reuse your hd and optical drives for a while untill you get more money and bump up to a sempron 3100+ combo for about $165 with free hl2 and farcry at monarch pc