I looked into this and the issue/high cost ($2000) is because the key fob has to be in the car for the remote start to work and that also keeps some of the accessories on so your battery ends up draining. They should come up with a servo controlled faraday box and hide that somewhere inside the car. I looked in to it but couldn’t pull the trigger.
I had a cheap off the shelf remote installed in my car and it works fine. The only hitch was I have to shut the engine off with the remote in order to unlock the doors. It did require a key to be hidden somewhere under the dash.