I'm looking for a calculator that will tell me the amount of fiat currency it takes to mine 1 BTC, both based on current conditions and on projected conditions within the bitcoin network (difficulty, etc). Given that the fiat currency prices for electricity / rigs vary, the calculator should give the low-end of the ratio.
Well, here's one approach:
Say you want to amortize the cost of a rig with say 3 ATI 5970s. That rig might run $1,250 (buying used), and consume about 1050W.
Each 5970 might produce 700 Mhash/s so the rig hashes at 2.1 Ghash/s. There is 12,700 GHash of current capacity on the Bitcoin network, all competing for 7,200 BTC per day. So that 2.1 Ghash/s will yield 1.19 BTC per day (7,200 * 2.1 / 12,700) -- and that amount produced daily is currently worth about $8.33.
If your cost of electricity is $0.15 per kWh, power that rig will cost $3.78 per day ($.15 * 1050 * 24 / 1000).
Amortize that rig over one full year, and the expense is $3.42 per day for the equipment ($1,250 / 365)
So using the one-year amortization your your rig costs $7.20 per-day ($3.78 + $3.42) and brings in $8.33 worth of bitcoins.
Thus it currently takes $0.864 to mine $1.00 worth of bitcoins assuming you have worthless equipment after one year, and that the "mining profitability" (the ratio of BTC/USD versus difficulty) doesn't change over the next year. Also, that is assuming there is no (zero, nada, zippo) labor costs.
Since nobody knows what levels these factors will be in the future, there's no projections that can be made reliably.
What is likely to happen is that the mining profitability for GPU miners will change dramatically, as the cost of electricity currently gives gross margins of 55% for a GPU miner with typical U.S. electric rate but for an FPGA miner those gross margins run from 90% to 95%. For ASIC, those gross margins might run from 98% to 99%. (at current difficulty and exchange rate levels). Obviously, as more FPGA s ship and once ASICs start to be produced, those gross margins will be falling dramatically.
The best deal around today is the GPU miner whose electricity is included in the lease. For that person, the hardware is cheaper than ever, and gross margins then are 100%. Many of these people are likely still acquiring more equipment, up until the point that heat removal and per-circuit capacity limits block further expansion.
But for the typical mining operator, the calculator above will let you do your own projections, if you might want to take a stab at a few different scenarios.