I'll tell you what I did and it wasn't that expensive (couple hundred maybe?)
I have an original working Ms Pac Man as well.
1.) Purchased a Ms. Pac Man to JAMMA adapter at jammaboards.com
2.) Purchased an iCade 60-1 board (from someone on here I think).
3.) Purchased a switching PC power supply (which powers the iCade) -- monitor, Ms Pac lights, fan, etc...all still run off the existing power supply.
4.) Since Ms Pac doesn't have any fire/jump buttons, I remove the existing control panels as I wanted to be able to return this to an original Ms pac cocktail at any time. They are held in by a handful of Phillips screws and the light panel by a couple hex screws. I then sourced two midway cocktail CPs. I found someone local with a couple junkers for $20, but I've seen them on Ebay, Mike's Arcade, etc...
5.) Mine were blank CPs so I purchased a couple joysticks (you could do top-switchable 4/8 ways, 4 ways, 8 ways, depends on your taste), 4 buttons, and 2 midway start buttons (mike's arcade). I also needed slide on connectors for the new buttons, joystick.
6.) Each Ms Pacman CP runs to a molex connector. I want to say one is 12 pin and the player two is 9?? I bought a couple molex connectors and a bunch of .093" pins. You also need a .100 header and pins to wire the fire/jump buttons to the iCade board. I think the total cost for the three molex connectors and pins was like $4.
Putting it all together:
1.) Using the existing Ms Pacman control panels as a guide, I basically wired the new control panels to the new molex connectors, and the two fire buttons from each CP run to a .100 connector that goes on the iCade board.
2.) The Ms Pac Man edge connector, instead of going to the Ms Pacman PCB now goes to the Ms Pac-Jamma adapter board, and the other end of that board goes to your iCade board.
3.) Connect the .100 connector from the four fire buttons to the iCade board.
4.) Take one of the PC power supply connectors and plug it into the iCade board.
5.) Lastly, drop a power strip inside the cocktail. Both the PC Power supply and the original Ms Pac Man plug go into the power strip. The power strip is now what plugs into the wall and turns on both.
6.) Enjoy!
It seems really complex, but it's not. I actually enjoyed crimping my own wiring connectors. I think the only "gotcha" is that the two lamps on each side of the cocktail also run through those 12/9 pin molex connectors, so I used my .093" pin extractor to remove them, and put them in the new connector. Otherwise you're going to have to buy two acrylic panels, light bulbs, bulb sockets, etc...
It sounds complex, but I'm a total noob and did those all in just a couple hours.
If you need more details/specifics and want to go this route, let me know. I can also post pics if you're interested.