> Im leqd to believe heatpump is a $50 device that manufacturers charge $2k for (must be more to it honestly).

Turning an AC unit into a heatpump is indeed pretty simple, but that type of heatpump doesn't work well when the temperature gradient is too high.

What you'd need to heat a car during winter is a "high temperature heat pump", which usually requires multiple stages, different thermal fluids, etc.

That's a much more complex and expensive system, not well suited to vehicles.