Where is the farm at, I am always looking for land close to home.
If you have a good farmer, farming it now just talk and work with him about staying on it. If not open it up to bids and take the best offer, best price isn't always the best for the farm in the long run. I would just post it in a local paper, the Register, and Craigs list. Land contracts are straight forward, but you can get a lawyer involved also. A lawyer also knows people looking for land and who to send offers too.
Don't use a management company, they look after their interest first and there are few you can trust.