As your Toyota Avalon has a V6 interference engine, a broken timing belt could cause some severe damage to your engine. Pistons and valves will bend or break, and you will almost certainly end up dealing with a warped engine and a large, four-figure repair bill.
What, exactly, is an interference engine? It's a piston engine that uses a four-stroke system of internal combustion and a poor history of precise performance. See, some of these engines are designed in such a way that the pistons and valves are at risk of interfering with each other through inaccurately timed movements. Piston and valve collision can cause extensive damage to the engine: Thousands of pounds worth of damage.
This is where the timing belt comes into importance. A well-functioning belt will prevent the aforementioned collision from occurring, while a broken one will only help speed along the destruction of your engine. It's possible to minimise damage by not restarting your engine after your timing belt breaks, but it's not always feasible to do this. If you attempt to drive your car regardless, you will be inflicting further damage on your engine and will be lucky if you can manage to pull over off of the road. More often than not, you can expect your engine to die within moments of the timing belt breaking.
To prevent this from occurring, it's recommended that you change your timing belt every 145,000 to 160,000 km travelled. Stories abound of people who ignored this recommendation and ended up breaking their belts shortly after eclipsing the 160,000 kilometre mark. These cautionary tales often have one thing in common: The driver lamenting over having to pay a ridiculous sum of money to repair the damage.
So in short, your timing belt won't break quietly: It will take as much of the engine with it as it can.
That's a lot of miles on your vehicle. Usually its better to change things at one time because it costs less than doing them individually. If it's the camshaft berrings, which usually means the engine has to be removed to replace, it might not be a good idea at present. I had those berrings replaced in one of my vehicles and I was charged $800.00 to remove the engine. Usually the timing belt or chain can be replaced without removing the engine and it only costs a few hundred dollars.
No doubt it is time for the timing belt to be replaced. I had one break on me in a Chevy sedan, and I was able to get it into a parking lot, but it was extremely difficult to steer. It had to be towed to the repair shop. I don't know about your other stuff... I would certainly get a second opinion and cost estimate. Don't tell them what the first place said, just ask for an overall inspection - perhaps there is a list of things on the make and model that the manufacturer recommends be done. Look into that on the internet if you no longer have the vehicles operating manual.
With the mileage and year of your car, either you have been lucky or Toyota makes really durable parts. Your timing belt should have been replaced at 90000 miles. Your timing belt is on borrowed time. Water pump is generally not a maintenance item. But like all other machinery, it has limited life. Most dealers recommend that you replace water pump the same time you replace timing belt because it is readily accessible. But if you replace coolant regularly, your water pump should last twice the life of the timing belt. I think that it is a good bet to leave the water pump alone. The cost to replace timing belt varies a lot even among the dealers. I was quoted $660 for Sienna. I would buy the OEM parts online and go to an independent shop. Your cost should be less than $250.
If a timing belt breaks, the engine will no longer work at all. If you are driving a car and a timing belt breaks in an interference engine, the camshaft stops turning leaving some of the engine valves in the open position. The heavier crankshaft will continue rotating by inertia, moving pistons up and down. Timing belt services can be costly on some cars, ranging into the thousands of dollars but at Winter's Collision Repair Winnipeg, you can get the best rate for the service of a timing belt.
Don't try and turn the engine over and over, just replace the belt or have it replaced. you shouldn't need all the other stuff. you should replace the timing belt as reg. service every 30k to 40k miles.