I agree with Jason that paying any upfront marketing fees is not advisable.
I have researched selling my Starwood timeshare, which is not based in Florida. If I decide to do it, I will set my reserve (might be low - depends how bad I want to sell it) and let the open market of eBay determine the price. It works well for everything else I have sold. As for escrow, there several companies to handle it, such as Chicago Timeshare Title. The typical rate for escrow seems to be $400 without title insurance and about $550 with title insurance. Perhaps TTS could provide you the name of an escrow company the specializes in timeshares.
I think that having a reputable escrow company is much more important than a marketing company.