If the farmer is using his own equipment, its usually $30-40/hr in my area. Also, fall can be a very busy time with harvest and all, you will have to be flexible, and able to live with the farmer's schedule. You should offer to pay for fuel, and your help. You might even consider offering your time for other fall chores the farmer might need done. He will not likely take you up on it, but will definitely notice that you offered. If he does take you up on your offer to help, consider yourself lucky. Do not offer your "expertise", just listen to what he would like done and do your best to do it well. Farmers HATE advice about thier operation, even if its good advice. If you can develop a good relationship with a local farmer, he can become your best freind when it comes to plots in the future.

Years ago, I used to offer to milk on sunday mornings, to let my neighbor farmer have a morning off every week. I had grown up with his son, and helped out on and off on the farm for years (you know - $1.00 per haywagon to unload, $5.00/day to help milk). I knew my way around the farm a bit, but was not an expert by any means. Even though its been 20 years, I would still feel comfortable asking to hunt that farm, and be glad to see an old friend.