Thanks for the advice. The cost issue we had wasn't the fan itself, but the installation that included knocking a hole in the exterior brick-face wall. In hindsight, I guess the extra cost would be worth it. Does anyone know roughly how much that's supposed to cost? Won't a vent allow cold air to come in?
I'm pretty sure our contractor used greenboard and the humidity-resistant paint; I checked with them and saw it for myself, but they did cut some corners. Is it possible the greenboard was improperly installed or defective?