If you want a 19" cabinet, then use a pre-existing one. They are EASY to come by (here is a hint, these boards aren't the place to find them the rec.games.video.arcade.collecting newsgroup and the klov.com boards are). Also, if no one responds to your empty cabinet request, then try asking if anyone has any project games for sale in your area (might be just as cheap as an empty anyway).
Now if you want a 25"+ cabinet. Then build one. A lot of operators still run these things, and a lot of Mamers want them, hence a lot of demand, which means that a good one is pretty hard to find.
You may also want to consider cabinets for black and white games. They are often in GREAT condition, due to the fact that they went off the arcade floor back in 1980 and never saw the light of day since. There is very little demand for anything black & white other than Space Invaders or Maneater, so the prices are very low. I remember recently a local guy had a real hard time selling a non-working Quadrapong (that was working but blew a cap), finally one of my friends got it from him for $25 (i had already turned it down at that price). The only downside to b&w cabinets is that they usually look a bit different than more modern cabinets and they often don't have marquees (just really tall glass instead).