Well, the options for emulation are pretty extensive these days. I haven't checked the MAME compatibility list lately, but that would be the first place to start. The chances are good that a title like Area 51 would work with MAME.
You would also need to rig up a minimalist PC in your cabinet in order to facilitate the emulation. If you have the know-how, you should be able to get the necessary components for around $300, maybe less. The biggest issue you will run into will be connecting a PC to the arcade monitor in your cabinet. Some manner of adapter will probably be necessary. Arcade monitors are designed to run at a lower horizontal frequency than the average computer monitor. (or even television, for that matter)