If you live in a rural area away from the big city that might be the perfect place to have a ride But it is huge to do that on your own.

Another idea is not to re-invent the wheel. There are rides where you fundraise for any non profit. In other words they are not centered around one beneficiary, you choose your own. I think the "Human Race" is one example of those. You may be able to find one near you or go to one:

www.marinhumanrace.org