[sassan]

First you want to make sure you have run the CPR code on the lens befor you conclude it is dead.

If it is still under warranty, (Usually younger than one year) you need the recipt. Otherwise you can get it fixed but at your cost. There are good repair people out there, but I will contact the dealer first.

How did you pay for it, a lot of time a credit card statement can serve as a recipt.

Many lenses have date code on them such as Canon L series that you can at least find out the manufacturer's date so you have a base for negotiation.
I get a written estimate before work is to perform on it, in case you chose to go for out of pocket payment, that way if it is very high, you may find yourself in a better situation to buy another one and dispose this on at what ever it brings as "Part / Repair only" on ebay with a bit of inflated Shipping and Handling....

Best of luck.