I've seen it mentioned a few times already in this thread that by artist selling their work on Ebay for cheep, it hurts other artists that are trying to do the same thing. I feel this is not true. The value of a piece of art is NOT with the process, but rather with the name.
The photographers that sell their work for $20.00 are stating that $20.00 is all their prints are worth, and rarely will anyone pay more. This does not mean that all photographers work are only worth $20.00, nor does that photographers "market value" of HIS work affect the market value of your prints.
In regards to being in a gallery and selling on Ebay at the same time, I think that is okay as long as your Ebay prices are the same or more as the print in the gallery. The other acceptable thing would be if you were selling cheeper prints that were not available in the gallery, such as special or open editions. Ebay can still reach a larger market of viewers around the world then a gallery can.