Lowering prices
I ran some number calculations for you just for fun. The calcs presume a monthly gross of $1,000, so if your gross is $2,000 then double the numbers, at $3,000 you would triple, etc.
I made the following assumptions about your existing situation:
1. Price is currently $2 for 4 minutes.
2. Half your revenue comes from folks who spend the minimum amount.
3. Half your revenue comes from folks who spend $4 per wash.
Based on your idea of lowering prices, I made the further assumptions of:
1. Half your customers who pay minimum startup only will continue to pay $2, and the other half of these folks will downgrade to pay $1.50 instead.
2. Half of your customers who currently pay $4 to wash will continue to do so, and the other half will start spending $3.50 instead.
Based on those presumptions, your $1,000 monthly gross will reduce to $907. This means you'll need to attract 10% more customers just to climb back up to your prior revenue levels. At $2,000 monthly gross it's that much worse.
If you think you can attract that much more business, say 20%-30% more customers, then you'll probably be on safe ground with your price reduction.
One thing is sure-- if you don't attract at least 10% or more customers your revenues will decline.
I'd really like to hear the results if you do make the change-- please keep us all informed!!