Can you weld?
If so, you coulf get some old junk wheels and modify them. I am thinking of some flat rolled steel, cut to the width of the rims, and the length equaling the circumference of the rims. Weld the steel to the edges of the wheels creating all steel wheels that will not dig into the dirt.
You may be able to pick up the wheels and steel for next to nothing and just have your labor and some welding rod into it.
Find out your TT bolt pattern and check with tire shops. They often have rims that were bent and replaced from customers vehicles. Those would be perfectly suitable for this use.
As for the steel, you may have some laying around, or a scrap yard... something that can be repurposed will do fine... Looks don't count on a project like this.