One key fob not working?
 

I have two keys so I still have one that works, but could this be a dead battery or something else? How much will this be to fix it? I push the button to lock or unlock and nothing happens

just open the dead one, get the same battery at your local radioshack... or buy from amazon.

Just change the battery. The battery is CR2032. You can get them anywhere, like a drug store.

Here's a guide if needed.

FYI any XX2032 battery will work. I was so confused on this at first but some manufacturers, Duracell for example, put a DL at the front. For an engineer that deals with part numbers often this was very confusing for me. I was expecting some type of difference other than just manufacturer.