This single card is about 100$ cheaper and seems to have better reviews than other brands of 2X 4870's Is this a smart move to go with 280GTX im really only using this computer for future games and MMO. Maybe Diablo 3 but right now i want to get warhammer online.
HD 4870 X2 (or HD 4970 1GB Crossfire) 100 fps
GTX 280 71 fps
HD 4870 1GB 64 fps
All excellent results, considering they are at 2560x1600 with high quality. Of course, in other games it won't be that great.
I'm personally a huge fan of Diablo 2 (best game ever, IMO) and can hardly wait for Diablo 3. I was told that Diablo 3 will work OK on my 8800GTX at 1680x1050, just not with all the eye candy and physics effects.
I'll buy a HD 4870 X2 when the game is released. I suspect it will be about $300 by then, not $530.
The problem you might have with getting 2x 4870s is that the 4870 only has a 512MB frame buffer. This can limit performance at high resolutions. Unless you are willing to pay to get 2x 1GB 4870s or the 4870x2, you should get the GTX280. Another possible issue with the CF solution is some people are sensitive to the "micro stuttering" that can happen with them. Might want to see if you can barrow a friend CF/SLI setup and see if you are one who is.
As for your other question, whats "decently priced"? If I were you, I'd figure out what monitor you are getting first before deciding on the video solution. For example, if you get a 22" LCD with a 2ms response time, your resolution will only be 1680x1050. Even the 9800GT/4830/4850 is more then enough to handle that resolution. I'd only worry about getting the GTX cards if you have a 24"+ screen, one that does 19x10/19x12.