18-105 repair cost?
I would second that advice with the caveat that you will probably end up with the same problem down the road. My 18-105mm suffered a similar fate--a drop and probably sand or some other particle contamination--that rendered the lens useless. If you don't want to invest in a weather-sealed zoom, then consider using prime lenses without any telescoping parts at the beach. It is clearly less convenient, but it will help prevent repeated reoccurrences of cheap lens failure. Just avoid changing lenses at the beach, otherwise you will be repairing your camera body instead!
If it was me, I'd just get another one. You can buy a factory refurbished 18-105 on ebay for less than $200.00.
I'd probably auction off the damaged lens for parts. I can't say for sure but I'd be willing to bet it will cost more than $200.00 to fix.
Sorry to hear about your misfortune.