FiNaL, when I started in 1990 my minimum cut/trim/blow ran $15. It was too low then and certainly too low now. Once I stepped up to a 36" commercial walk-behind I realized how much the small lawns were costing me. Since most of my first clients were elderly raising prices was like pulling teeth and since they were there when I needed them most (starting out) I ate the losses.Sure did hurt though to spend an hour for $15 or $18 bucks when I had $35 cuts that I could burn through in a half hour or so.
If I were to take on those accounts again today, $25 would be my minimum. Keep in mind most of those properties were of a "push mow only" size. Even if I could make a few passes with the 36", no way to get it in the backyard.
Use one or two of your better clients for references. When you explain your minimum price be sure to sell them on your quality work, if you're doing a top-notch job they'll notice. Once they've seen that and you establish a good pattern for reliability/consistancy they'll feel better for choosing you over someone cheaper.