Does a video card for a Mac Pro always have to be the Mac version of that card?

I see here that my Mac Pro (Early 2008) is compatable with:
ATI Radeon HD 2600 XT
NVIDIA GeForce 8800 GT
NVIDIA Quadro FX 5600
ATI Radeon HD 4870

It looks like in many cases there's two versions, and the mac version costs about 10x as much on ebay and in stores. Is that accurate, or is one of these models mac and pc compatable, and therefore the laws of supply and demand work in my favour?

(fyi: I just want the cheapest one, I don't do heavy GPU work)

666sheep said:

OP, you listed cards for Mac Pro 2006. Right list is below (in your link).

Click to expand...

Thanks, I just copied the wrong list. Edited original post to reflect.