I offered $40 a month (1x a day ) "Unlimited "
wash pass for close to 20 months. It was a $13 wash including
Armor All Carnuaba wax. I have to tell you, more than half of the people went everyday. THEY WILL WASH IN THE RAIN. I quit advertising it and eventually phased it out. My average monthly ticket on that program was about $6 a wash.
I now offer pass codes on that same Wash $55 for 6 washes. I sell these now and kick myself for not ending program when I bought in August 2018. My average ticket is now well up over a dollar a car by not offering up monthly's.
They will clog up the bays on sunny days and the wear and tear on the machines is not worth it in my opinion for a couple thousand dollars before you wash a car.
I have a 3 bay IBA 2 4000s and 1 Tandem.