Water pump

How fast does it get hot? How hot is it actually getting? Does the fan seem to be working?
Why did you replace the pump and thermostat? Because it was overheating before?
What do the radiator hoses feel like when it gets hot, are both the same temperature? One hot one barely warm?

Do a pressure test on the cooling system, you can usually rent them from auto parts stores. If the system holds pressure then it could be a partially blocked radiator. If it will not hold pressure then it is more than likely you have a head gasket starting to fail. To verify that run a combustion test, also available at the parts store.

It's not that hard but it isn't cheap. It depends a lot on who does the work and how much they charge as well as what is actually wrong. It could be as simple as a blown head gasket or it could be a cracked block or head. The problem is that you can't look inside the engine and say exactly which it is.

I would run the tests, then if it looks like a bad gasket, check with a couple shops about doing just the gaskets, and what they would charge to swap out the engine for a used one and for a "remanufactured" one. Then make your decision based on those numbers. Just be sure to get written estimates if you proceed farther.