Hello. I purchased used, and now would like to add keyless entry. Is this something I could do myself, or would I need to get dealership? Also, I wonder what kind of cost I am looking at.

 

Moved your post to a separate listing.

What brand and model of keyless system? Did you get the instructions with the system? Decent brands offer phone support for installing.

Does you car have electric locks? What year of car and option model such CE, SE, LE, XLE?

This can be a DIY installation and many owners install it themselves.

For professional installation suggest finding a stores that sells and installs their own and third party products. This would be cheaper then the dealer.