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

i see here mac pro (early 2008) compatable with:
ati radeon hd 2600 xt
nvidia geforce 8800 gt
nvidia quadro fx 5600
ati radeon hd 4870

looks in many cases there's 2 versions, , mac version costs 10x on ebay , in stores. accurate, or 1 of these models mac and pc compatable, , therefore laws of supply , demand work in favour?

(fyi: want cheapest one, don't heavy gpu work)

 

a regular card not work, @ least not without bit of hackery. reasons why, , options are, read thread:

http://forums.macrumors.com/showthread.php?t=877441

 

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