Granted, I've never built a pinball machine but I'm not sure how the calculations work out to how 100k could build only a single machine, but say 110k could not build 5 machines, in which case you'd just need five "investors" to give you 22k each. or 120k to build 10 machines, 12k each from 10 people.

all that said, if you have the know how and the time, why not put together the prototype sans license in the meantime...

IANAL but if you're just making a singleton machine and not for financial gain, I'm pretty sure you can basically use any license you want, look at all the themed homebrews. so maybe your initial asking price should be much lower, considering how you don't actually need the license at this point.