Not if you do it yourself - radiator is about 150 and the expansion tank another 50. You might be looking at a couple hundred in labor if somebody does it. Best time to get a coolant flush as well. 740's just have a real bad problem of having unexpected failures of the radiator once you get up in miles, even if thtis isn't the real problem, it's a problem.
If you can't see any evidence of chalky looking stuff around the radiator neck or seams of the expansion tank, my bet is on the valley pan - the v area under the intake manifolds. It will pool there and if small enough burn off, its a PITA to look around down there but worth a check.