I looked into this, and it would be $1K-$1.5K at least with install. Its a lot of work if you want integrate backup camera, steering wheel controls, sirius satellite antenna, headliner microphone, etc, etc..Why not get a replacement head unit, lots of fascia adaptors out there. Then get a double din pioneer unit with CarPlay. (If your car supports a double din)
Versus $90 for my Car Thing which was an adequate solution. My iPhone is paired to my car, so I just get inside and have a spotify UI for picking songs, playlists, etc.. and its accessible to my passenger too. I really like my Car Thing.
I can afford a new car, but it seems wasteful when my 2010 Mazda CX9 is still running beautifully with no issues and 167K miles. I don't like buying things that depreciate in value, so I run my cars until they're inoperable.