Leaves take many times the work of just mowing. Each yard is different, depends on the amount of trees and etc. It is very easy to screw yourself if you don't know how to estimate, I know I did early on. Warning, people will take advantage of teenagers and people with little business experience. I really can't give you a number without being in your shoes.
Some advice I will give you is start running your business like you actually paid for ALL of you equipment & vehichles. Obtain a business license which is usually required by your city. Report your earnings and pay taxes. Point is run it like a legitimate business. This way you will learn how to properly run a business and the real costs. I know you probably won't do these things but if you do you will be much wiser earlier in life. Don't strive to be the person who does it for the cheapest price.