[bumby]

>By the time most cars need a replacement engine and transmission, the only thing available is likely to be used/salvaged or rebuilt.

There are plenty of engines that go back 30+ years that can still be bought brand new. You're probably right about the "whole new drivetrain" not being able to be installed for under $6k though (depending on what you define as a whole drivetrain). But even a rebuilt engine can fairly easily last another 100k miles, depending on the vehicle and the quality of the rebuild.