It's not the cheapest, by a long way. For instance, my mate has just got GT5 XL and a wheel off eBay for £23. Compared to my DFGT it's, well you can imagine what it's like.
For me there is 3 wheels worth buying, the DFGT, the G25 and the G27. They go up in price respectively, I got my wheel from Argos for £99. The G27 is a lot dearer than that, but people say it's worth it's money. For me, a casual user, the £99 was more than enough, and the wheel is amazing. I cannot fault it, the pedals are a bit cheap, and you don't get much feeling from them, but the wheels outstanding.
It takes a lot of getting used to. It took me an age to learn how to drive in GT with a DS3, then when I got the wheel, I had to do it all over again, but I did gain time.
In short, if you want a properly decent wheel and don't wanna pay the earth then the DFGT is perfect. Take the plunge, you won't regret it.
Also it is compatible with other games, I used it on NFSHP. It wasn't much good, lol, it must be better with F1 games.
DO IT! DO IT! DO IT!