I currently service an Enterprise rental car agency. The work done on the cars is minimal but they pay decently for the what I do. My current service for rental cars is a quick wash (ONR), clean wheels and tires, and dress the tires. The interior is a simple vacuum and wipe down with hyper dressing for a nice shine. I clean all the windows and they pay $30 per car. I can get done with 2 cars per hour and make $60. On an average day they have me work on 6 cars.
About once a month, they will give me a few nasty cars and pay $75 for a more extensive detail. This includes a wash and one-step (XMT 360). The interior is wiped down with citrus cleaner, and dressed as before. The carpets are given a quick extraction. Although the car doesn't turn out perfect, it is clean and fresh. Total time spent is about an hour and fifteen minutes.
Each time they receive new cars, they pay $75 for a sealant and carpet/upholstery protectant to be applied. This makes future clean up more rapid and easier to achieve. Before selling a car, they pay for a full interior detail and one-step exterior polish/seal which works out to about $100.
As with dealerships, they are cheap to work for, but they do offer consistent work which can be done using their water and electricity so there are benefits. On average I spend about 4 hours a week at the Enterprise, and make about $200.