black "smoked" 19" rack-door

Middle Atlantic, if you're using one of their various standard height racks. I don't know if you'd consider it cheap though, I think my 78" door was ~$450.

Depends on the size of course - I did a search for "smoked glass rack door" on Google, and the 11th search result had a door for their 20 space oak rack (35" high) at $139.50 (didn't put a link here, since they're not an AVS sponsor, and didn't want the admins to have to remove the link).