If you think you can do it, go for it. Your charge sounds reasonable, based on adverts I see in the local paper. The real advantage is that there is virtually no start-up cost.
There might be other openings; some local shops may already, or might like to, offer a similar service and you could try to get in on that network. Offer to demonstrate your skills to them.
Unless you are very lucky, it will probably take some time to develop a business; you might like to consider what income you need and how many hours you will have to sell to reach that level. Remember that you are in competition with your old self and with the neighbourhood kids.
I wish you good luck with whatever direction you choose to take.