Something else to consider is what an individual FFL will charge for the transfer fee. One local purveyor of fine firearms charges $35, while another pawn shop just 10 minutes away will charge $20. Two guesses who I go to.
Another web site to check out is GunsAmerica.com. They recently revised the software running their operation, and it seems to have settled down to actually giving you what you were searching for.
On just about any of the brand-specific sites (GlockTalk, CZForum, CZShooters, and SIGforum to name a few) there is a classifieds section for buy/sell/trade of both firearms and accessories. Only the firearms (except for .22lr conversion units, which have no receiver) need to go through an FFL for transfer, unless you can do it as a FTF(face-to-face) sale.