based on where you are you will get variations for a couple of reasons.
Till they see it, they don't know how rusted up everything is.
Sure it is a 2/3 year old truck, but if you don't ever wash it down after the salt on the roads, they may need to replace several things.
So high price so you aren't shocked when they say x part needs to be replaced because it is too rusted.
Low prices are to get you in the door and then say oh my, x and y need to be replaced that will be 800 bucks. (while most places only say that if you need it, there will be those that say that even if you don't)
Not saying all of them will be like that, but that is the norm.
Eitherway you are going to be pissed if you go to the 200 dollar place and wind up spending 700 bucks.
Ask around, find out who others go to and don't have a problem with. Word of mouth is a huge thing for shops.
If like the others said you are willing to try and do it yourself, you can save a few hundred.