Existing fenced arena has steep grade - anyone completely re-leveled?

Hello, I have an existing arena that was put in approximately 20 years ago by someone else. It is approximately 260 x 100 and fenced. It is graded short-side to shortside fairly steeply. You can feel the slope while riding as in going up and down the hill, and the momentum that the rain water accumulates from the “top” of the arena completely washes out the footing at the “bottom.” The base is destroyed on this ring with rocks having broken through everywhere. I have another riding area in much better shape, so this one is currently not the focus to fix. However, I would like to eventually rehab the area.

I dream of hiring someone to grade this thing to level and crown it properly so the water drains to the longsides (instead of from top to bottom). However, I’m guessing we may not only need some sort of retaining wall, but I may also have to remove the fencing since the elevation is likely to change dramatically. I’m sure the cost on this would be astronomical, but I’m tempted to just get a quote to level it and work on re-building a base one step at a time.

Has anyone taken on a project like this?