Well to me it looks cheap (if I got the concersion right ). But it's a pretty old card so I really dont know. How about a GTX 460 or maybe 5770, don't know, putting two old GPU's in CF doesnt seem like a good decision in my opinion.
From what I read 3870X2 in CF have some problems, like not being able to turn AA on etc.
Flisker if your budget is really only 1000 Koruna (~$50) then I guess your best off doing what you already decided. Just know that you are getting an older card (two of them) that won't support some newer technologies (like the latest directx). You'll be able to play most all games for a while in the future though.
If you can go for a little more money, get a single 6850 right now and then in the future buy another one. The one 6850 will be way better than two 3870s, if you can afford it.
Also your Chipset is probably not he best, for crossfire the 790FX ( Nowadays I think it's the 890FX, but your Mobo is probably older) is the best, so if you chipset is say a 780 it will also decrease performance.
Maybe you should go for the 9800GTX and don't worry about Drivers, Game bugs etc. in my humble opinion