I bought an Industrial 4000 several years ago and paid $4,000 for it. I immediately replaced axle seals, wheel bearings and brakes but since then just a cylinder rebuild and an occasional hydraulic hose. It had three new tires so I just replaced one front tire. Once you get comfortable with the machine you will find it very handy.
I've put in a septic system, well and done some excavating with it. I also use it for snow removal and hauling firewood. I'm considering putting in a pond with it next.
I respect the age of the machine and know it's limitations and I expect it to last me for eons. If the engine and transmission work well on the machine you're looking at I would consider everything else secondary.