You ALWAYS replace the water pump when you replace the timing belt in a case like this, simply because the pump itself doesn't typically cost a lot, but they are going to do most of the same labor. If your water pump goes bad in 2 weeks (which is certainly possible with 90K on the car), they will have to charge you for the same exact labor all over again, making your $100 water pump installation $500 instead. That is why it is recommended. Kind of like, you wouldn't replace your transmission and stick a clutch with 50K mi on it back in there again so you could pay them to do the same labor again in 6 months if the clutch went.
If you were to pull your injectors yourself, it would still cost you $100 to have them cleaned/serviced. Like MDS said, if they are just running a cleaner through your system, it probably isn't worth the $100, though they are going to hopefully run a MUCH stronger cleaner than you can buy. If you figure the cost of one injector is more than $100 (I had one die a few months ago and it cost me $240 for ONE injector), and if you've never run a FI cleaner through the system yourself, it is probably worth it, especially if they are goinig to pull them out and look at the spray patterns.
You can also purchase and replace the spark plug wires yourself and save the labor they are going to charge you, since it only takes a few minutes. Don't be surprised if they cost a lot just by themselves though. Wires should be replaced periodically, even if you can't visibly see that they are bad. If you've never done it, I would replace them.
Timing belts and timing chains aren't the same thing and are generally applied to different types of engines. It isn't designed obsolesence exactly. Belts are used because they are cheaper and quieter, at the expense of not lasting as long as a chain. They work just as well as chains though. Even top fuel dragsters use belts, not chains, and we are talking about 7000HP (really big belts

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