The SP50 would need to price in the range of 120-150BTC to compete
Surely you mean 80-90?

No way. Bitmain is selling 0.25w/gh at about 1.4btc/th.
This is 0.15w/gh and includes power supplies, but also a 'bulk priced' device, so i would expect 1.2-1.6btc/th.
That said, I'm not buying any hardware until my bitcoins are worth at least $300 again. Otherwise you will never earn back the btc you spend (like buying hardware with $100 bitcoins in mid-2013)