Could be possible to buy an logic board of a mac pro from apple, or whatever of his parners?..did anyone know and orientative price?

I have seen people buy them at the place i work at (re-seller + authorized service tech center) and they aren't very cheap, usually 800+ for a logic board. most likely more for a mac pro one out of warranty

This one on ebay is $450, but it looks like it doesn't come with the memory riser cards (in other words, you'll need to find one of those too - maybe two. I don't know if it requires both to be installed).

um...very expensive for 800, i was thinking in buying one, adapt some pc case, flash a 7300 gt to get working like the original one, and buy the cheapest pair of quad core xeons, of course with a good amount of memory at cheap prices