I offer this on both residential and commercial. It is surprising how much easier it is to sell to residential customers over business customers. You would think it would be the other way around. How I price it is, of course, complicated. It varies according to soil load, use and other conditions. I approach it on a percentage of the initial extraction charge, but then have to adjust that number according to other considerations too cumbersome to describe in a post. What I would suggest you do is this:
Do NOT allow a customer to talk you into starting a maintenance program without a full extraction cleaning being done first.
After this initial extractions (at full normal pricing) set them up on a program of choice and base your pricing upon the factors that came into play during the initial extraction ... like difficult areas to clean or access ... parking or entry problems ... anything that effects the time it takes for you to perform your scheduled tasks.
Residentially, I sell almost all my accounts based on a six month cleaning schedule and can usually price them at somewhere between 12 to 15% of the initial extraction charge (paid monthly), but you can't do this with commercial. A commercial program is just too complicated for blanket statements. I have commercial accounts that I clean monthly, so of course these are priced higher. I have other accounts that I clean quarterly, but I am in there weekly changing out the matting. So, you can see how hard it is to describe, or even formulate, the pricing.
The best thing to do is focus on your hourly target and factor in your expected time until you can titrate your rates based on experience.
Sorry I couldn't be of more help.