V6 LE camry 07 82,022 miles. 4 Rotors needed? Rear brake scraped loudly and suddenly.
$645.00 for a complete brake job. Did I get hosed?

Likely. I'm surprised you needed new rotors. Many mechanics say all rotors need to be resurfaced, which is not true. In fact, it can create lateral runout (LRO) problems, if it's not done properly. They usually turn the disc to the axis on the lathe, not the spindle's axis. This can create all kinds of problems that didn't even exist before. In reality, it may have only been the rear wear indicator contacting the disc, to let you know the pads were worn down too far. Rear disc brake pads frequently wear out much faster than front pads, since they are much smaller. For $645, I hope they changed all of the brake fluid. I believe you overpaid, especially if none of the calipers had to be replaced, which is unlikely.

Unfortunately, many manufacturers are using what I would call "barely there" components during initial construction.
I'm not saying that is always the case, but I know your brake rotors were fairly thin when new.
This keeps down the costs of manufacture plus shipping costs.
Think about how many cars any manufacturer builds and ships and you will see how it can add up. I recall an instance where a major airline began using just one less olive served on their in-flight salads and over the course of a year saved thousands of dollars.
Keep in mind, if rotors are measured before the work is done, they may well be within spec but if they "need" resurfaced, they will then probably be below spec and thus need replacement. Like Txgreasemonkey stated, unless it is absolutely necessary, I don't resurface rotors.

2004 GP 3800 engine 127000 miles. Should I have it replaced it or wait until it breaks? Cost estimate?

My experience with Toyota brakes is you got almost exactly what most people face. Actually, 82,000 miles was pretty good for OEM disc. The disc by itself can run $60 to well over a hindred each, add to that pads and labor and I think you got off light.

That engine should go 300,000 miles, especially if you use SAE 5W-30 full synthetic engine oil. Change the oil and filter every 6,000 miles or 6 months, whichever comes first. For the car to last that long, you also need to change the transmission fluid and filter every 30,000 miles (Dexron VI).

I am a big fan of Toyota but bad things start happening long before 300K. 2 Highlanders, 2 Camrys and 1 Solara so I like my Toyotas fine but twice, around 150K, had a crack in the exhaust manifold and it was not cheap. The engine should last but I need the whole car to last. No trouble with alternators or water pumps so I will keep buying them but wish they'd up their warranty

With vehicles of that quality, and good preventive maintenance, you should be able to go well beyond 300,000 miles. I've seen it many times.

Yep nut around 150K the new models start looking pretty sexy.