...all kidding aside...
If you pay $4K for a MAME box, even brand new, you are either really rich and throw your dough away and not feel it OR you are a moron. So DON'T DO IT!
You can build yourself a brand new spanky cabinet with all the latest and greatest components for about a third that cost OR if you wanted to go with a pre-built, I am sure there are MANY people on these forms that would build you a brand new cabinet for about half that price.
Do you have a link to information about this $4K cabinet?
I HIGHLY recommend you spend some time here and find out how fun, rewarding, and EASY it is to get in to this hobby and you too will soon spend more time WORKING on them than PLAYING them and not because you have to, but by choice.