I personally wouldn't use gemm (most on there are over priced, well those I seem to want) or popsike to price a record. I would rather use the price guide I think you are referring to...and have done. I would ask on the forums first, here or Rare Soul Forum. Popsike I would have a look but out of curiosity rather than anything else.
I've been toying with the idea of an interactive database where members can edit every section, titles, matrix numbers, writers producers, general info and prices...its just getting round to doing something about it.