Can you check around your area to see what others are charging?
A lot of things come into play when determining price.
Size - if it's small, you may need to charge more since it's not a full days work.
Distance - What's your plan for charging for distance?
Area condition - If it's hilly, rocky or full of other things that may damage your equipment, you should charge more than a nice simple, flat field.
You'll need to cover depreciation on equipment, fuel, maintenance, insurance, travel costs... as well as make a reasonable wage for yourself. I'd think somewhere between $40-60 per hour (but you need to consider the aforementioned points before specific pricing) is in the ballpark.