But according to the wiki, the FPGA hardware is so expensive, that I could barely make it to 200 Mhashes/s with my budget. So it would be smarter to just let my desktop PC do the job, with ~150MHashes/s (I tweaked it a bit). My computer runs 24/7 anyways, so the power consumption might be slightly higher, but yeah.
I think your underestimate how much power GPU use relative to how little 150 MH/s returns. You have one of the worst electrical rates combined with one of the most inefficient cards.
A little exercise:
A) find out how many BTC you will earn per month @ 150 MH/s.
I will earn ___________
http://www.alloscomp.com/bitcoin/calculator.phpB) find out how much energy you will use
GTX 580 = 250W.
250 /1000 * 24 * 30 = ?
I will use ______ kWh per month
C) Find out your monthly power bill (just for the GPU not the rest of computer)
(from B) kWh * $0.28 per kWh = $ monthly
I will spend $ ______ per month
D) Find out your price per BTC produced.
$ (from C) / BTC (from A) = cost per BTC.
I will end up paying $ _____ per BTC to mine.
Still it is your money. Hash away.