Depending on the type of small trees and what size "small" really is, you may be able to sell the trees and let that person clear the land for you. 20 acres may have enough trees to make it worth it for someone to harvest them.
Be careful if you go this route as many tree guys have a attendance to leave a mess behind - make sure you get in writing what they will do and how much they will pay. It may be, to get the land properly cleared, you may have to find someone who will do the clearing in exchange for the wood - you won't get any money this way ... but it won't cost you any money, time or sweat if you can work this out.