So 600 hours at an average income of $100/hr rental gives a $60k in sales for 3 years per machine. Sounds like a lot, right? Then subtract the purchase price $9k, gas $6k, maintenance $2k, insurance $12k, overhead $10k, dock space $3k and misc $6k, add back in the $3k sell price. That machine only made a profit for the owner of $5k/year. That's why the rental business is tough and only works if you have at least 10 units and can keep them out at least 4 hours per day each 6 days per week. Insurance is mostly to blame, 10 times higher than it used to be 15 years ago.
Anyway, rental units are great buys if you don't mind them looking like they were dropped from a plane and then hit by a train.