If you want a legit Mappy coctail thats going to be a tall order. You can buy the midways cabs like Steve suggested and convert it though pretty easy. If you want to make good use of the space and dont mind not having originals pcbs you can get the arcadeSD board and put it in, its a pretty nice board and works well in the coctail configuration.
$150 for a working Mappy board is reasonable, they are only going UP in price.