Airplane ownership and operations costs are probably higher than in the 90s, but the factors driving that are diverse, and I'm not sure they'd apply in any meaningful way to self-driving cars.

A lot of the regulation that drives the cost of planes up won't apply to cars because of the different economies of scale.

The most popular light aircraft in history is the Cessna 172, and since it was introduced in 1955, only 43,000 have been built. Ever.

By contrast, the most popular vehicle on the road today in the US is the Ford F-series pickup truck. Since being introduced in 1977, Ford has sold 26 million of them. So roughly 600x as many as Cessna has sold 172s over a period of time 20 years longer.

The US market alone was responsible for 17.5 million new cars and trucks being sold last year. Globally, it's approaching 100 million per year. Pretty incredible economies of scale available with that kind of market.

The late Bill Machrone coined Machrone's Law which stated that "the computer you want always costs $5,000." This hasn't really been true for 5-10 years. You can build a $5K computer but you have to really push it. But saying that the figure is still at least $2,500-$3,000 is probably fair.

That's not accounting for inflation - $5000 then was more like $10000 now. And a bare-bones minimum machine for running business software (i.e. no color graphics or floating point hardware) was still close to $2000 (more like $4000 in today's dollars). So, roughly speaking a maxed-out gaming rig today is about as affordable as a bare-minimum box in 1990, without even accounting for the massive difference in absolute power.