All I can say is, you are very lucky she only wants 20% commission. That is quite low. Pick out a few that you are not attached to and see how they do. If they sell quickly, maybe your price is too low.
Only you can say what a fair price would be. Look at it this way - if someone gave you $1000 you would be ecstatic. If you found out one sold for $5 you would be miserable. Keep working in from both ends.