Well, that's a bit of my time gone (re)looking into GeoHot, patent trolls, and now comma.ai.

Comma.AI by George Hotz sounds very interesting, it's basically a $999 "comma 3x" smartphone with an OBD-II connector and a $99 wiring harness that can add an equivalent of a Tesla Autopilot to many cars manufactured in the last 10 years (even Tesla's own cars, too), for a total cost of $1098, whilst being OSS and available on GitHub, and — get this — even having ssh access to your car! Optional cloud subscription plans are $10/mo for your own SIM, or $24/mo with bundled cellular data.

Sadly, it does NOT have an equivalent of Tesla Sentry Mode yet, https://github.com/commaai/openpilot/issues/29912, which is kind of unfortunate, because Tesla's own implementation of Sentry Mode is using 250W of power — depleting the entire 80kWh battery from 80% to 30% in like 7 days (".5*80kWh over 7 days" = 238W) — openpilot would have been a nice alternative at what'd presumably be around 5W or less ("40kWh / 5W" is 333 days).