My town has a population of about 2,000 people. There are five dedicated car washes within a 10-mile radius of my house, with two more under construction.
Biggest cost is the startup and then employees, with an occasional big maintenance repair.
Buying cleaning products in bulk? The cost will make you feel cheated for what you pay for a quart to a gallon.
I get that, i used to service a small-ish car wash, and the amout of times something broke or didn't work or the cost of osmosis filters alone was staggering to me. Always thinking about how many people would have to wash a car to just get that money back.