Car washing business when I was about 10 or 11.
I sourced out the best products, learned how to clean cars properly and had flyers printed. Went door to door doing sales and left flyers with people.
I charged between £2 and £5. I can't remember exactly, but I do recall the cheapest was £2 and the full with a wax and wheel clean was around £4-£5. I even calculated my margins and made sure it was all profitable before I started. Costed out my products and created different tiers for the service.
This would be the early 90's, so it was good money. I needed to carry a little stool so I could reach the top of the cars.
I was only doing it part time(weekends), so it was just "pocket money", but it was fun and I made what was pretty decent money for that age.
I started off just doing basic washes for £1 to build up enough to get the good products and have the flyers printed. I always loved business and creating products.