Looking for suggestion on a Gearbox replacement/sub

[GeeTwo]

You may want to consider gearing down all or part of the way using pulleys and belts or perhaps by clutching a small wheel to a large wheel; these solutions are less expensive than a gearbox.

[DaveL]

To solve the problem of shooting targets...
Build carts to carry your targets and drag them around the parking lot with a car.

Hopefully you will only be using rubber tipped arrows!
Dave