I think it's a great idea, too. There is a self-service dog wash at a groomer that also boards not far from here. I think it was $12 or $15. they supply everything, soap, towels, and they have a power dryer. Sure cuts down on time drying a husky! The elevated tub and noose is great. I really like that they supply the towels! My only complaint was that it wasn't exactly "clean" by my standards, I had to do a little "clean-up duty" before washing my dog. She operates it several nights a week, they are always busy, you usually have to call ahead to book time.
Contact your local Businessman's association, they usually have a group of seniors that will help you with info and advice to start a small bussiness.