Back of the envelope math on breakeven point:
Current hash rate: 7.2M tera hashes
If I invest in 15 terabytes of hash, then I will receive roughly (15/7.2M)*12.5 (block reward) * 2750 (current btc price) * 144 (blocks per day) = $10.3 per day

current electricity = $4.20 per day.
$6.10 per day breaks even with $1950 investment after 320 days.

Assume hash rate continues to increase faster than price, breakeven point is probably closer to 500 days. I'm ok with 500 days if my contract can go forever, but if it ended after 2 years in the best case scenario and earlier in worst case scenario then maybe I wouldn't buy.