Hi. Please consider a miner with 38GH/S hash speed.
How long does it take to get 100$ from mining ? With 7/24 working. Assume electricty is free.
Even with free electricity you will never make 100 dollars because of difficulty increasing.
If difficulty averages around 15% a month you will make around ~17 dollars in 2 years and not growing from that with free power.
If difficulty averages around 10% a month you will make around ~25 dollars in 2 years and not growing from that with free power.