I’ve bought low miles (less tha 50K) ISC and mechanicall 8.3 engines for $5000. Put the ISC in a truck instead of rebuilding the engine in it...much cheaper. Add another $4-5,000 to swap so still less than half of a rebuild. I still have the 8.3 as I sold the truck it was the spare for. Good used engines are out there but you have to search and it can take months of searching.