Soft footing for riding that isn't expensive?

We might be building a spot for my horse at a friend's house. They have a field that is about 1.5-2 acres. We would only be able to afford to build a fence around the perimeter, and a shelter.

I would like to still be doing arena work, some jumping in her field. She needs soft footing, because she has joint issues in her leg, and hard ground puts stress on them.
The ground is slanted downhill, and we wouldn't be able to afford to build a fence for an arena for quite awhile, probably never.

Do you have any suggestions how we could put a corner of the field with soft sand or mulch, wood chips that is moderately cheap?
Possibly a type of fencing that costs next to nothing, to keep her from scattering the footing everywhere when she is out in her pasture running around?
Thanks a bundle ahead of time!

Search hog fuel in your area.

Is that good footing?

Everything is going to be expensive because you have to have a way to haul it in. Unless you have your own dump truck or dump trailer, it will be costly.