G'day Whitestonestar,
That would be a hard question to pose an answer to. It would all depend on what Fossils you were chasing really? Are you chasing Opalised Fossils or Rock/Petrified Fossils?
If I were backed into a corner to give an answer, then I would simply say that they are generally worth what someone is willing to pay -to a certain extent. It would be hard to get some collectors to part with a good Fossil (no matter the monetary offer), and on the other side it can be very difficult to get a buyer to pay anything for a good Fossil at times.
There's almost too many variances unless you can narrow down the specifics, but that can generally be done without too many drama's.
Hope that's a little help.
Kindest regards,
Shauno.