I'm concerned that I don't see a back end to your funnel here. Looks like you only have small, medium, and large of one service.

Rather than concentrating on discounts and discounting methodology, why don't you look at Cost of Customer Acquisition?

If you knew that number, you'd know what you have to make to break even.

I also think you're hamstringing your lifetime customer value by limiting yourself to one service. There's nowhere 'up' for your customer to go.

If you knew the CAC and LTV of your buyers, then you would know exactly what you had to charge. You'd understand even taking a loss on the front end because it lead to a big profit on the back end would be a possible strategy. But right now, you don't have a clear picture; that's why it's so hard to decide.