In today's "take no responsibility" society, I wouldn't even consider letting someone else use my land for ANY purpose. but defintely not for something with a high risk, (compared to say hiking on my land).
The Op suggests a pay per use, once you take money for permitting use of your land, your assuming liability. Even if one were to design a "liability waiver" that would, (if it was upheld in court), waive the liability for the rider, (meaning the rider couldn't sue if injured), but the rider can't waive liability for others who are not "party to the agreement". So basically while the rider may not be able to sue they can't sign away the rights of their family to sue the land owner.
I belong to the provinces largest ATV club, and we have a $5 million dollar liabilty policy, on all the trails, (including those on Crown land), that we manage. We even have a policy to cover liabilty for our board of directors etc.
The owner of the Raglan Pits, had posted no trespassing signs on the property but never took steps to "secure the property and enforce the no trespassing", a rider was technically illegally riding on the property and was injured. The owners were sued sucessfully. Durham Regoinal Police now make regular visits and charge those that they catch on the property.
So unless, someone really doesn't care about their financial well being they would be reckless to permit something like this, on their property