Markup for gems after setting?

I have recently gotten into ebay and have found some nice little
inexpensive faceted gems, ie. topaz, citrine, ruby, and the
occasional sapphire. I think for most of these that I have
purchased them well below the market wholesale value for loose gems.
I am wondering if anyone has any idea of a website to visit or
other reference to see current estimates for prices of faceted
gemstones and how much I should mark them up to once I set them in
my custom silver pieces.

Thanks all, this is such a wonderful forum!
K