Sorry in advance for this being an opinion rather than experience, but if the soils and construction are quality, I would imagine the cost of pumping would be some fraction of a typical well or sump pump. It can certainly be done, but it then becomes an issue of cost. I assume it would run intermittently as opposed to continuously. Most would depend on how high you're pumping it too. There are better resources than me on this subject, but I think it is a tough one to answer without knowing the height, distance, and frequency. With that said, frequency can't be determined until the pond is built because you don't know how well it holds water. All ponds "leak" so that is one factor that will have to be guessed.
