Very few PC monitors support the standard 15khz output of jamma boards. If you are lucky, and I mean very lucky, you've got an old Commadore PC monitor. Those do support 15khz and work very nicely with game boards. There are a few other old monitors that support 15khz, but so very few that the chances of finding a working one any cheaper than a used arcade monitor are slim.
To display 15khz RGB on a tv you need an RGB to Composite converter. There's a few choices here, but nothing really "plug n' play". Some people hack specific game console adapters, some do it other ways. Google for "arcade supergun", you should get some ideas.
BTW, a "supergun" is a device for playing arcade game boards on a TV, it usually consists of a control panel, power supply and video converter.
Regards,
D