Was quoted $720. for an '04, ES330

It's a little too much I think.

Ayup, that's more than a bit high, but ask to be sure they may not be replacing some other parts while the front of the engine is apart...oil seals, tensioners, idler pulleys, water pump, etc. Since the engine is apart, the cost of replacing those is mostly the parts themselves with minor labor. But I'd also check another place or two, and look online for coupons for discounted sevice...20% off a $500 bill is worth the few minutes online hunting for it.

BTW, it has a timing belt, not a chain.

Good luck!