GSO, I think you handled the situation correctly. Hopefully you will receive payment with no problem. Life is a learning experience, and although I always THINK I have made all the mistakes at least once, new ones continue to crop up.
Next time you will realize you need to give people some idea of the costs involved before you start a job to avoid a problem on down the road.
I also don't think you were out of line with your fee, which works out to about $35 per hour. If I were mowing for 14.5 hours, I would expect to get roughly twice that much.