Here are two video cards, with the small form factor backplate, that I tested today for you in that workstation. I like the Quadro cards for reliability, and one is the Quadro 600 and the other is the Quadro K600. Well within your price range..... I got these both virtually new off eBay for less than $80.00 USD each with careful shopping. This is the Windows Experience Index scoring, in W7, with max score possible of 7.9 for each category. Same box... only the card was changed:
The K600:
