Doing the math, starting to mine still paying off?

[Axez D. Nyde]

I was planning on setting up my own bitcoin rig just for the fun of building something.
But I am a student and on a small budget so this project has to at least to amortize itself. Just did some calculations to see how deep down in my wallet i have to reach to get this thing on its way.

I already own: a MoBo with a Celeron and 2 Gigs of RAM. It has one PCI-e x16 and three x1 slots. Two PCI slots as well but I don't want to utilize them for now. Also I own a HD5870 and a 350W and another 450W PSU. The costs for these hang around 380€.
But to get this thing on its way I want to add 3 more HD5870s. Why? Because they have a good Hash/Watt rating and electricity is expensive where I live. I mean really expensive. And I don't own solar power panels or wind turbines or anything  . I would also go for HD5970s but they are rare right now. And HD6990s are too expensive.
Three more HD5870s cost around 170€ (used ones, yay!) so I add 510€ to the list.

Now I can't pop them in my case, too, because it would get too hot I'm sure. The warm air from only one card is already stressing the PSU that is mounted above the mainboard and sucking in the hot air from inside the case. So I need PCI-e extenders. Four x1->x16, three of them with molex power-cords so that I can use the 450W PSU on them cost ~70€ in total (shipping included). And then I also need the PSU starter adapter thingy so that both PSUs start simultaneously. +8€

That is a grand total of 968€! Bazinga!

Now I would estimate the power consumption of this baby to be 4*200W for the GPUs and another 100W for CPU, MoBo, and fans that I eventually put in there. (Now one of the PSUs is probably gonna blow, maybe add another 80€ to replace the 350W thing with something (cheap, but) decent, like 550W or 600W)
...anyway 900W at 80% efficiency is gonna suck ... 1125W out of the wall. That means I will be paying 189€ more with my next monthly utilities bill. (0.25€/kWh, per four weeks or 28 days).

Oh and now the sweat part, suggested income!
I would say a good estimation of the Hashrate would be 1600 MHash/s, that's 400 MHash/s per card. So according to this calculator http://www.alloscomp.com/bitcoin/calculator.php at the current difficulty of 1888786.70535 I would be averaging 23.84 BTC per 28 days.
And at the current currency rate of ~ 7.10€/1BTC (that's 10$/1BTC) I would then earn 169€.

But OH WAIT! I need to pay the electricity bills, so what I really earn is 169€ - 189€ (-some fees for the pool) (-some less income if difficulty increases) = -20€ OR EVEN MORE!

[nmat]

Well, yes. That's pretty much it. If the price rises (to $14 for example) you would have profit, but it would take a lot of time before getting the investment back.

But the price could also fall...

[floeti]

Be aware of the fact, that this is no less speculative than joining the stock market. Maybe your investment will amortize, maybe not, maybe it will amortize but not before 6 months or even a year. No one knows that. I think you should only do that, if you seriously can afford the time you have to invest to keep your rigs up and running efficiently.

[timmey]

A little more than a year ago, someone bought a Pizza for 10,000BTC https://bitcointalk.org/index.php?topic=137.0

Just saying you shouldn't see Bitcoin as a way to make instant profit, it's more like a long term investment.

[TheBanker]

You need a place with cheaper electricity. Otherwise, it's going to be really hard to make it work for you.

[stellan0r]

with your system you can make the safe bet on 4 x 440 mhash/s and a power consumption of round about 0.8 kWh!

Getting a high quality high power PSU would probably help you if you find one that has an efficiency level of over 90% at your power consumption! this would lower your overall use of electricity.

what do you pay for 1 kWh?

[Axez D. Nyde]

I pay 0.22 to 0.25 €/kWh here. depending where exactly I'm firing up my pc.