[Jesse Z]

Does that estimate include labor to R&R the core? If not, $280 to rebuild a little heater core is ridiculous. In fact, if your heater has already given trouble-free service for "a few years" then that makes me even more suspicious of the integrity of that shop. Visit another radiator shop, do some shopping around for a better price. Or since it's lasted this long, don't worry about it. Heater core failures usually aren't catastrophic they'll spring tiny leaks and give you plenty of warning.