I am in the same boat as you where in figuring operating costs. I relied on the mulcher manufacturer for guidiance but ultimatley I will have too figure it out for myself. I purchased an extra set of teeth when I bought the head so I have them. The teeth can be turned 4 times during ther life. The oem says about 300 hours out of teeth but I am over 100 and have not turned them yet. A set of teeth are about 1000.00.