This depends on your cabinets monitor. If you have a high-res monitor capable of 31khz signal and has a VGA input, that saves you a lot of $$ and hassle because you will be able to plug the PC directly in at 640x480. Otherwise if you have a standard resolution monitor, you need either an ArcadeVGA or VGA to RGB converter, with the card offering better results but seems to me like its much more of a hassle to deal with. The last option (and probably cheapest) is to buy a video scaler that will also convert VGA to RGB gracefully with a lot of control and extra options that the ArcadeVGA card or standard converter wont have. Check out Extron Emotia, they are very cheap and generally on ebay once in awhile.
The rest of the cost is all up to your electronics skills. If you are a wiz with a soldering iron, all you need is a keywiz or similar interface product, a cheap audio amp and a jamma edge connector, all totaling around $50 or less depending where you shop. If you do not have electronics experience, then you will have to go the IPAC route but my knowledge is limited on that but its more costly to begin with.
Good luck!