I am today literally working on a case study for Party Rentals.
What do you want to know?
We have some clients using us - SwiftCloud - for eDocs i.e. agreement, waiver eSign etc - also client management.
Good biz, not exactly passive but somewhere in the middle - pickup and dropoff, stuff has to be cleaned (kids..); weddings, kids jumpy houses birthday parties, corporate parties etc.
Good margins, but there is some asset depreciation, the houses don't last forever.
Upside - not that much to start, like $5k can get you going even though probably more like $20, then like any biz it takes some work to get the momentum, but then the referrals and repeat biz starts flowing.
PM if interested, I'll put a case study up on YouTube soon
What do you have an unfair advantage at?
i.e. some background, probably something you take for granted? A head start vs others?
Setup a service business first. $5k is not that much and it'll go fast, but you can start a service biz for like $2k that banks $$$, then spend another $1k-2k on marketing and advertising, and you'll be off to the races.
"boring" businesses - gutters, handyman, even Christmas lights can make $$$ if done right.