I know that it's virtually impossible to freely prospect or collect in the area (claims, quarries, etc, etc) so I've never considered a collection trip there.... until recently.
I like to attend the rock/mineral/gem/fossil shows and always look forward to the Fossil Lake/Green River Formation displays (and have purchased specimens).
One of the better vendors I had the pleasure of meeting (I forget which show) was Robert Bowen who owns Wyoming Fossils.
He offers a pay-to-dig service (and other services) at his quarry and was curious if anyone has visited it. It's closed through the winter (seasonal) as the website states but if I can afford to.... I'd like to hit it sometime in the future if it's worthwhile. $120 for 8hrs sounds kinda steep but I really don't think it's too bad considering the likelihood of leaving with treasure.... provided you still have a good back and are motivated.
Here's a link to their website, I'd really like to hear from anyone who's been there (or similar) if possible: Wyomingfossils.com
thanks!