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.

 

The dealer may sell something that is a plug-in installation. There should also be aftermarket units available. Conduct a Google search.

These units are offered with and without out alarm

Many owners install the units themselves, the job should be pretty straight forward.

Cost, perhaps $150 for aftermarket more for a for Toyota offered product.

Toyota offers good products and if availabe might consider this route even if more expensive.