Also note that the monitor may work but not very well. Alot of arcade machines are left on for long periods of time which usually results in the static images burning into the monitor screen. I've also come across monitors that have defects such as a permanently bent or stretched screen which is no longer square.
If I was in the market for a low cost cabinet I would try looking locally first and be prepared to lug the machine back to my place myself. Are there any old machines sitting unused in an old arcade or shop? If so make an offer, you may find a shop owner that would be glad to get rid of an old machine (provided you take it away yourself)