Keep investing or cut my losses? Sole F85

I bought a used Sole F85 for $50 that "needed the belt lubricated". I get it home, watch some videos, do some troubleshooting, and it most likely needs a new walk belt and a new controller board. I can do the replacement myself, so if I have to replace both I'll be in for about $500 in parts. The motor tests good, the console and hand controls all seem to work fine.

The unit is about 10 years old. This will be my first treadmill. I'm about 6'3 300lbs so I need the belt size and weight capacity. I will only be walking, likely up to 3.5mph, no running.

Do I invest the $500 and fix this one, or do I cut my losses? I probably wouldn't drop $2,000 for a new one, so I'm either going to spend the $ to fix this or find another one used.