I just ran numbers for Tesla Cybertruck. Depending on gas vs electricity prices, a "Tri FSD" CT, built to million-mile specifications, will pay for itself on gas savings by 0.5-1.5M miles.

I think "free truck" operated to design specifications constitutes cost effective.

You have to factor in the time value of money though. Car purchase price is an immediate cost while gas and electricity are costs over the life of the vehicle. Your average personal cars only gets driven about 15,000 miles a year and thus those gas and electric costs would be spread out over decades to reach a million miles. Probably still cost effective considering the average truck isn't that much cheaper though.

Too bad you can't buy one...

*yet

You can buy nuclear cars yet either...

No one is actively trying to build nuclear cars however. Additionally, no one has a prototype nuclear car, because that is a stupid and very dangerous idea.

There is a prototype cybertruck, and Tesla is about to announce the location for the factory to build them. It will be either Tulsa, OK or just outside of Austin, TX.