I never replaced the radiator on my 98 pathfinder. But I also maintained it properly by replacing the fluid every other year. Radiators are usually something you replace when it needs to be replaced. But you do need to replace the fluid at the very least every other year.
If there are actual stress fractures then it might be worth considering.
Replacing the radiator is NOT difficult. I don’t see how the labor is so high. But the radiator does have to be removed to replace the timing belt (at least removing it will make the job a lot easier).
We can’t tell you what they are replacing…You have to do that…Get a detailed list from each of them to find out what they are replacing…then compare the two estimates. Don’t assume anything. How are we going to know. In general an independent should be cheaper because labor costs are usually a lot cheaper.