I sell my site at 3 months of revenue and I see difficult to sell them on flippa. I have much more success on Ebay...
Seems some of your domains able to make money , why not you estimate and predict every domain you able to sell and with list your domain how much you can earn it and cover the cost. I think you can earn more compare to charges for the list because some of your domains do have some nice keywords.
Its danger to sale intangible asset with ebay. To be honest, Flippa is the best place i ever thought to buy/sale website properties.