That's not bad at all. You counting the PSU? My PSU cost 150-250 each, which is comparable to the mobo, cpu, ram, hd and case put together. so you are looking at about $400-500 for the non-GPU parts, times 7 = $2800-3500. That leaves around $4500-$5200 for the gpus. 21 gpus at about $200-250 each, what kind did you get? 5850, 6950? Either way your MH estimate is pretty accurate if you OC and run aggressive command line args.
I built three rigs from scratch. I bought three used gaming computers. One computer didn't work so I bought a replacement motherboard for it, then I fixed the motherboard added the power supply, CPU, memory and that gave me my seventh rig. So I have Three computer in cases and 4 sitting open on the table.
The Power Supplies were the most expensive part. One was $250 and the cheapest was $190.
Did you factor in the cost of shelving/computer storage, surge protectors/electrical wiring, fans, and A/C units? You are going to need at least 20,000 BTU of cooling for that if you live anywhere south of Maine. That all should run you another $1000 plus, easy. Bring your total capital cost to more than $1.14 per MHash. Then you got to factor in rent, unless you already have a sunk cost mortgage on a house with a usable workshop, garage, or extra bedroom. Recalculate with all that and you might find closer to $1.50 per MH.
Not counting any of that. Just wondering about the capital. I own my house. Most of my rigs are in my basement where it used to be nice and cool. For about $30 I added 40 amps of outlets to the basement. I haven't needed any cooling, just fans on all the open rigs. I'm burning an extra 2.9 KWatts for about $340 / month.
ok fail sorry.
