The dealer will surely rip you off! Here's my easy method:
1. Push the silver button to open up your key.
2. Take a small flathead screwdriver and insert it into the notch below the VW symbol.
3. Gently but firmly pry up the side of the fob (it will detach at the middle, into two parts) as you pull at the fob from the top and bottom ends. Don't pry up too much; just enough to let you pull the key apart.
Now that the keyfob is in two pieces, gently pull apart the bottom half (the half without the key), revealing the battery! The battery pops right out.
4. Take the battery to your local drugstore and find a replacement. If, for some reason, the remote functions won't work after you replace the battery, there are instructions in your owner's manual for recoding the key.