I'm pretty sure those 15 mpg mega trucks and SUVs will be cheap soon.
If you drive 12,000 miles / year and get 15 mpg, $3/gallon is $2400, and $5/gallon is $4000.
What is an additional $1600 / year for a car you're already paying $12,000 / year for (assuming $60k, 60 months)?
So while demand might decrease (particularly if EV pickup truck production capacity grows rapidly), I would not expect $60k vehicles to quickly become "cheap."