usb interface kit cost to install Gen III

I would like to install the USB kit in my Prius Gen III I have Nav.
The dealer said it would cost $580 for kit and installation.
What are other dealers charging?
What happens to the warranty if I buy the kit online through this site and take it to an independent to install.
Also will the dealer install the kit if I buy online and take it to them?
Will that still keep it all under warranty.
I would appreciate input.
$200 for the unit and about another $150 for installation sounds far more acceptable than the price quoted by the dealer.

What your dealer quoted you sounds very high. $200 for unit is about right, but the $150 seems high. There have been instructions posted on the forums, and it doesnt look like it should take too long. So, I think the $150 is too high

I would save that money and DIY. It is seriously really easy and will take about 30 minutes. I swear the hardest part is removing a bolt cover piece under the arm rest.

I had difficulty putting on the license plates so I think I shall pass on DIY.
However, if I have the instructions for installation then I can find someone who is not mechanically challenged to do the job.
Do you have the instructions for installation?
Thanks

Not sure, the salesman said that my Pkg 5 had it, showed up without it and I bought the part ($240) and made them install it for free ... looking at the invoice though I believe that the normal charge was around $100, that is what they deducted so that I only paid for the part.