Bought a showcase house from a local builder in late-2016. Paid $146p/sf (this included the lot). Smaller lot than what you'll find in Castlegate or some other SOCO areas, but nice, higher-end neighborhood. Thought I got raked over the coals, but looks like I was below average based on price ranges others have quoted in this thread. I wanted a spec so didn't focus or research on price per sf quotes.
And yes, the local builders are banking $$$ right now. Margins are healthy, inventory still relatively low, and buyers coming in willing to pay $300K+. As long as there are no corporate development companies coming in to knock out huge developments and drive lot costs down, this will continue. Have found BCS labor on average, to be ~10% higher than what it is in Houston (supply/demand).
Only other way I see around the high custom/spec prices is to find a GC with enough trades, knowledge and an LLC, that they will do it for ~10% margin (most spec/custom guys are targeting 15%-20%, which is an industry average for the south Texas market) on the side, as most banks will not let you GC yourself unless you have the LLC and track record. Have several friends who have gone this route...it's always a roll of the dice as to how much time the GC actually has, their and yours expectations, and the quality you'll end up with/time it will take. If you're aiming to keep costs down but still want custom, this is probably the only route to go in this area.
If you are financing it yourself, that's a different story and you can use whom you want.