Then go for one of the GeForce FX series, which are really cheapening up. The 6xxx line is still really high end, and therefore expensive. GeForce FX 5200 are in the sub-$50 range right now. I've been running one for a few years and have been able to play Half-life 2 with barely any hitches. Doom 3 is another story, of course, but new RTSes aren't quite as intensive as those games are. You could even go higher up in that line and spend a bit more if you want something that'll still hold up for a few years even in the market of the high-end games like Doom 3 and such.