I had a similar problem on my 2013 e70. Do not pay the dealership $1800! Buy a plastic trim removal kit so you don’t gouge your interior and the inner door handle is like $20 on Amazon and they have many different trims available. You’ll also need an Allen key, maybe 6 or 8mm, don’t remember which, and look up door handle replacement vids on YouTube. Tape the surrounding leather to play it safe.
It’s really a $30, 1.5 hr TOPS job. It was super easy to do, mind you I did the passenger’s side and had no electrical components in the way at all.
US Amazon links:
Trim kit: https://smile.amazon.com/dp/B01L8GHB7O/ref=cm_sw_r_cp_api_glt_fabc_R3X6SYPE8NVHQY7NM1VN
Inner handle replacement example: https://smile.amazon.com/dp/B07C6L1GKC/ref=cm_sw_r_cp_api_glt_fabc_KWGNAV051EC34XY0ESM9?_encoding=UTF8&psc=1
The $250 installation seems like a lot. Not that hard to do yourself. I
bought a panel removal kit from Amazon for $13 and I was able to
complete the installation.
Tresalto Auto Trim Removal Tool... https://www.amazon.com/dp/B01L8GHB7O?ref=ppx\_pop\_mob\_ap\_share
I don't believe you can downgrade the firmware. Installing the version 70 first is a requirement for the "official" android auto. I paid $162 for the USB cables and dock ( https://www.amazon.com/gp/product/B07KRPSRKH ), and $10 for the trim kit ( https://www.amazon.com/gp/product/B01L8GHB7O )
I found the instructions to follow here: https://forum.miata.net/vb/showthread.php?t=679114
There's a link to an 'hdrive' site, find the NA firmware, put them on a USB key (16gb or smaller) and follow the instructions to the letter. It's easy.
Then find the folder for the videos of the cable install, find the closest match to yours. Also easy.
Firmware took an hour (mostly sitting and waiting). Cables took an hour in my 2018 CX-5.
Both were easy as far as anything technical I've ever done. Very easy. Just take your time, follow each step carefully.
Below is exactly what I used and the video I watched. I would just make sure the camera is compatible (this link below is for 2015-2017 Sonata model years)