Electricity costs don't figure into it anymore for ASIC miners for bitcoin. The electricity cost is negligible compared to the value of the bitcoin. The cost is in the up-front cost of the hardware to mine with.
For Litecoin and other scrypt coin and other altcoin, electricity costs may also often be dwarfed by the profits. You gotta do the calculations, and there are many fine websites for that. Coinwarz, coinchoose, wheretomine, etc.. Since you have "free" powar, you can enter $0.00 for your power cost.
If you are new to cryptocurrency, I suggest you ignore bitcoin and get into the altcoin markets. You generally do this by getting an inexpensive but relatively new computer with PCI-e slots, and then buy some sick video cards to hash with. I suggest the following cards:
RADEON 7990, 7950, 7970, 280x, 290, and possibly 290x. Check
https://litecoin.info/Mining_hardware_comparison for more info.
There are also some new and interesting developments with CUDA miners for NVIDIA cards, but if you are a newbie I suggest you go with one or two of the RADEON cards and get the hang of it before you delve into the dark and fuzzy corners of the cryptocurrency underground.
With $3000, I would build a rig like this:
Three (3) 7990 from ShopBLT or TigerDirect or somewhere: ~$2000
ivy bridge motherboard + modest cpu (celeron G1610) + 16 gb RAM (4x4gb) + SSD: $120 + $42 + $158 + $80 = $400
A really crazy awesome power supply: $300
http://www.newegg.com/Product/Product.aspx?Item=N82E16817153155You will need to piggyback an extra ~700 watt power supply for the 3rd card: $80
3x powered risers: $50
Milk crate case and box fan: $50
keyboard/mouse/cheap monitor = $100
good surge protector = $50
Linux Mint 13 LTS = $0
TOTAL COST = ~$3000.00
TOTAL KHASH = >4000Note: If you want a more powerful CPU for the purposes of gaming, I suggest you go with AMD, not Intel. You do have a 3k budget, after all.
Note: You may want to go with 4 to 6 of the cards listed below, instead of 3x 7990 cards. 5 cards should easily fit in a wide milk crate case:
6x 7950 >3500 khash (7950s are the most energy efficient and easiest to manage heat) [but make sure your motherboard has 6 PCI-e slots]
5x 7970 >3500 khash
5x r9 280x >3500 khash
4x r9 290 >3200 khash
...depending on market conditions.
I suggest you not "mix and match" too much. It is OK to get 4x r9 280x and throw in 1 r9 270x, but I wouldn't include r9 cards with older 7xxx series cards in the same rig, or you're likely to run into driver troubles, especially if you are new to this.
If you don't want to go with a bulky milk crate (or otherwise custom roomy much airflow) case on the road, I suggest you buy 2 of these:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131543along with the rest of the liquid cooling system, and be prepared to wait a while to see any profit. (~1800 khash)
ALTERNATIVELY, you can get 2x 7990 plus 2 water blocks, remove the original coolers, replace with water blocks and rest of the expensive liquid cooling system (LCS) and if you tweak the cards right you should be able to get 2800 khash/s out of the rig. All of this is possible for under $3000 if you aren't silly about your CPU and motherboard requirements. Maybe I'm being a little silly about the RAM requirement... you could probably get away with 8gb, I'm not sure. As for the $300 PSU, you can shop around and/or piggyback 2 power supplies on your main, and probably save some money up front, but talk to a pro and they'll probably recommend a very nice power supply like the one I linked.
I'M JUST A NOOB!
Cheers and happy trails!!!1
