About the electricity i have calculated the expense for Each month i spend 12$
Are you absolutely sure?
paying 12$/month means you're paying about 1 cent / Kwu... That's really, really, really cheap...
I've entered 1 cent/Kwu into coinwarz and only entered the power usage of the miner, not the overhead (like cooling).
At 1 cent/Kwu, the power will cost you about $9.5/month... Include a bit of overhead here and there, and some basic lighting, cooling, maybe a raspberry pi, and you're paying $12/month (at very least, the cooling will probably cost you more).
http://www.coinwarz.com/calculators/bitcoin-mining-calculator/?h=4730.00&p=1293.00&pc=0.01&pf=1.00&d=286765766820.55000000&r=12.50000000&er=767.22000000&hc=400.00I've "invented" a price of 400 USD for a second hand S7 + shipping + customs, and imagined you'd already have a PSU, shelves, cooling,...
In this imaginary situation, you'd break even in 140 days... IF the difficulty would stay the same, and the btc price would remain steady. Since the diff is still rising (AFAIK), and i can only assume you don't have a PSU, shelves,... it'll probably be (a lot) more...