That kind of game would be quite addicting indeed.
Thought I would rather not have a limited number of games a day (which could be abused with mules) but paying an small fee (for example: 100 FPs).
Yes, exactly as those machines actually go: you pay a little something for a chance of earning a greater prize. This could be a neat FPs sink!
And in those machines some of prizes are cool, but others not so much. So pretty much the same could be done.
Same as the real machines, it should be tricky and there should be a chance of failing and getting nothing.
Or instead of these machines, an slot machines would be cool too!
(And probably way easier to code

)
An idea for prizes would be Wild Knuffel items, current Digging items or daycare coupons. I mean: items which are already quite random in value!