I'd think more like $20 and I get a sticker. After all, I'd be advertising for the
project anywhere I took the sticker.
In terms of how many people swarm a campground, it really depends on where you're located and the season. I've camped in campgrounds where reservations are by draw a year in advance and jammed full, and I've camped in campgrounds where there have been two small camping groups and 20 empty sites.
Most (all?) national/provincial/state parks now have a reservation system, which is helpful in preventing 100 people showing up at the end of the day trying to get into 2 sites, but also, for me, takes away from the free spiritedness of a road trip. If you have to make a reservation, you have to get there on a certain date. If I ran a campground, I'd allow reservations for probably the greater percentage of sites, but always make sure that 20% or so were available for people who just find themselves there.
If this campground is going to be in your community supported forest, and there's a campground of 20 sites, I'd set aside half or three quarters to the members, and allow those sites to be reserved by the fully paid up members, and leave the rest to first-come-first-serve non-members or members who don't want to reserve, during whatever the "season" is. If your forest is somewhere with freezing weather in the winter, you
should really be aware that most of the general public are not going to want to camp in the cold, and that a lot of government parks offer very cheap or free winter camping (with no services.) If you have no services in winter either, why should someone stay at your place instead of their place?
Also, are you allowing truck campers/RVs? As a sometimes truck camper, it's annoying to be told at some RV places that we're not welcome, since there are apparently laws in some places about trailers always having to be movable i.e. on wheels, and as most truck campers don't have all the self-contained services as RVs. So if your campground offered sites to truck campers but not RVs, I think that would be a selling point to disgruntled truck campers.