Hey, actually created an account to reply to this. Been lurking around here for months now. Anyway.....
I've run FFXIV on everything from a 8800m (laptop) to GTX580SLI and several cards in between. Truth is you don't need a super huge video card to run this game and have it look good. At the bottom of the range I would suggest is a Radeon 4670 (I have two of these) and that does struggle a bit. With your budget in mind you can go with a lot bigger card than that.
Personally I would suggest something like a Radeon 7870.... http://www.newegg.com/Product/Product.aspx?Item=N82E16814150605
It's at the top end of your budget but it's latest tech and has 2GB of vram. Now when the gtx670 or 660ti comes out that might be a good choice too. A 670 will most likely be $399.
At the bottom of your budget would be a 560ti 448core.... http://www.newegg.com/Product/Product.aspx?Item=N82E16814130738
This is a good card for the money. It is a generation back, but it will still do DX11 and all that.
Couple other things I wanted to point out as far as Crossfire and SLI. One is that if you're planning on getting a second card go with the latest tech, which is currently the Radeon 7xxx cards and the Nvidia 6xx cards. Reason is I've found a lot of times if you wait too long that particular card will go out of circulation and you won't be able to find a second one.
The second issue is Crossfire vs SLI, especially with FFXIV. If you run full screen then it's not so much of an issue, but I found that only SLI will run in windowed mode. Crossfire will only run one card in windowed. Now, that may have changed, but as of a year ago it wouldn't work. I'm currently not subbed into FFXIV so I can't test it on my 4670 Xfire rig. I suppose I could check it with the load up screen. If anyone has any newer info on this please chime in.
Edit: one other thing, make sure you have enough power supply to run whatever card you're looking at. They usually list that in the video card specs. Edited, Apr 19th 2012 9:09am by VG1