Why go to all this work if you are only going to offer this to fleet accounts?
Do you really have enough electricians etc that will pay 4-6x a month to wash unlimited? The average unlimited tunnel customer only washes 3x/month so it seems hard pressed that the majority of fleet customers would pay anything more than that(3x) for self serve.
I like your ingenuity in looking for a workaround but the way you are trying to do this sounds like a lot of back end administrative work for a small reward.
How do you handle declined credit cards?
How do you handle insufficient debit card funds and alert the customer that you haven't received payment?
I used the original Wash Card system with rfid. Tags the size of a quarter placed on the windshield. I made my own rfid. Reader that attaches to my ACWS . I am using this setup for unlimited auto washes but it could easily be used for SS. Bays. I picked up some of these for $100 each off the forum. Each one controls 2 SS. Bays or 1 SS. AND 1 AUTO bay. You could do 2 SS. Bays with readers and 100 tags for under $1000.
Just out of curiosity, why would you want to offer unlimited washing at a SS for 10 or 15 bucks a month? Is it on the assumption that people may use the wash less than the cost of the plan would give them in a pay per wash situation? Would you require a yearly subscription or monthly and cancel at any time? I am sure that every one of my customers that are regular customers and therefore would be interested in such a plan, would definitely be getting the better end of that deal by far. A lot of them spend at least half that every visit and these are people I see at least once a week and quite a few more often than that. Maybe my location, being right by the ocean and having car washing weather pretty much year round, is why people wash frequently. Even at $25 a month, I think it would be a wash at best. (no pun intended) I have a few people that wash their car just about every day.