I've got both wheels, and i'd seriously recommend the Momo wheel if you are going to use it for the PC only. I've raced with both, and quite intensely too. The DFP takes ages to setup for your likings, while the Momo has standard profiles in every racegame. Its a simple click in the game to make it feel the way the developers want you to feel it. Although the DFP has 900 degree rotation, i've never used it on anything else then GT4. Jeroen Ursem still drives with the DFP, and he also just uses the 200 degree mode. The Gearflaps of the momo are easier to use aswell, and i think it looks better then the DFP.
mediamarkt sells them for 119 euro at the moment, which i think is quite a bargain for such a quality product.
Momo Racing
Logitech DFP
If you still want the DFP, it uses an usb port indeed, and you can download drivers both from logitech, or from the wingman team (which i recommend) If you buy it second hand, make sure all calibration works the way it should work (test before buying!) Since the dfp pedals are known to have problems with the gaspedal only giving 90%.
The G25 is out of your budget
Logitech G25
But i do know a good steeringwheel which hasnt been mentioned yet, but should be really good, the Thrustmaster Rallye GT (RGT)
Some of my mates from the ZAC2 league use this wheel to, and are very satisfied with it. Also, it
is the official steeringwheel for GTR2! With a new price under 100 euro, it is within your budget!
The Thrustmaster Rallye GT
btw, expected release date: latest friday of september