Yup, below $20 is a good price for commercial inside the outer loop of Houston, but I wouldn't exactly call their HQ location downtown (about a 25 minute drive from downtown, 50 min with traffic according to Google Maps.) The $28-$32 for property is on the western side of the 610 inner loop, west of downtown and considered the most desirable areas to live and work inside the Houston Metro.
I've been doing a lot of research recently into the Houston RE markets, both residential and commercial. My wife wants to work at the Texas Med Center, we may be relocating to Houston soon.