Here are the differences in cost.
Most shops will look at what it takes to remove and replace an item (R&R). They will look at book labor. This provides a basis of what it should take to replace the item.
All shops have different labor rates in the country. $100+/hr in bigger cities. Sometimes as little as $60/hr in small towns. This in itself will drastically change the overall price. Let's work with 10 hrs for ease. $1000 at one shop $600 at another.
The other thing you guys are not comparing is the kit itself. Let's use upper control arms. To replace a stock control arm is easy. To set up an Icon adjustable is a completely different story. You're now dealing with multiple parts within a control arm. I will easily charge someone an additional hour to set up a control arm. The tech now has to apply anti seize to 8 different threads to set up an Icon arm. Not including the time it takes to thread each part in and measure for equal distance.
Let's deal with coil overs. There is no adjustment for the factory system. If I install your coil over out of the box, can you guarantee your truck will sit level? Probably not, seeing the multiple threads started for unlevel trucks. Now a tech has to adjust the coil overs.
And lastly, how about the alignment. We all know there's only 4 adjustment points from the factory. Add adjustable control arms, now we've got unlimited movement from the top and bottom. Add to this, the knowledge of what to do with those adjustments. I'm sure you guys have read even more threads on this subject.
I'm not saying that all shops are fair with pricing. But talk to them and ask for an explanation of charges. It's your right to know what they're charging for. This wil also give you an idea of wether or not that particular shop knows what they're doing.
