For reference, my build cost $1400. That is for an i7 930, Gigabyte motherboard, 6GB RAM, HD5870, 650W PSU, 640GB HDD, and Antec 900 case. I already had OS, mouse, keyboard, and monitor. I did later replace the single monitor with 3 new ones for Eyefinity which added about $450 but as that wasn't part of my original build I'll leave it out.
Going with your idea of 3D you'll absolutely need to go with an nVidia graphics card, preferably a GTX4xx series which are pretty expensive. You'll also need a 120Hz monitor which are more expensive than 60Hz monitors and you'll need the 3D Vision glasses. There's no way you'd be able to fit all that into $1300 unless you ditch the i7 and go with an AMD Phenom X4 CPU platform and cut way back on the graphics power.
What it comes down to is your priorities. How badly do you want 3D? If you want 3D you'll need some serious budget change or a whole platform change to AMD. If 3D isn't so important you can cut it and keep your i7 and high end GPU. As far as I've heard, WoW isn't too hard on graphics cards, but Crysis definitely is and you'll need some decent power to push Crysis at high settings.
For your graphics you'll most likely end up spending somewhere in the $300 to $400 range, especially if you plan on running 3D as you need more power. nVidia's GPU's typically run for higher prices than ATi cards and as nVidia is the only vendor with 3D support, you'll need one of their cards.
The i7 is somewhere in the range of $300 for the CPU, $200 for a good motherboard, $160 for 6GB triple channel RAM, so for the core PC you're looking around $700 as a high estimate. You still need a hard drive/solid state drive, a power supply, a case, a video card, possibly an OS, and possibly a monitor. If you go with $300 for video card that puts you at $1000. That gives you $300 for HDD, PSU, case, monitor, and OS which is pretty much impossible unless you go with bargain bin cheap components which you will later regret.
My advice is this. If you want to go with a 3D setup, wait a little while longer, get another paycheck saved, do whatever it takes to afford a bit more hardware. With an extra $200-300 you could get your 3D setup and a nice one at that. If not you'll have to cut a ton of stuff and won't get a very good build or you'll have to cut 3D and go with a basic monitor. If you don't have this option, I'd look into AMD's platform as the Phenom X4's can be had for much less than the i7 which gives you more room. As with any gaming computer, the graphics card is the most important, so try to get the best one you can.