Is $9,000 to repair a cracked detached garage foundation a fair price?

I recently bought a home with a 20x20 detached garage that has serious concrete slab foundation issues. The settling ranges from 2.5-5 inches across a 10ft span from the center of the garage in multiple directions, and there are cracks going in multiple directions. This is largely due to poor drainage and tree roots. I plan to install drainage and remove trees regardless of the foundation solution. I'm trying to decide if I should repair the foundation or rip it out and replace it. I'm also curious if polyjacking is an option for this level of cracking, as the company I got a quote from doesn't do it. I'm also open to demolishing the entire garage and building a new 20x20-20x24 structure on a new slab. The garage was likely built in the 1950s-1960s. It's currently bare with just framing and wooden siding, as I ripped out insulation and drywall due to water damage and pests. The electrical works but isn't great. The garage is slightly leaning due to the foundation, but the wood is mostly solid except for one sill plate.