Isn't it? An average car gets ~25mpg and travels ~14,000 miles per year. That then adds up to a total of $480. Hard to estimate the average value of a car on the road, the average used car sales price is probably a good proxy (misses some value for first-owner cars, overvalues last-owner cars) which gives $28000 (2021 was likely abnormally high and this'll actually drop some, but still). So then, you're talking 1.7% when parent was asking for 2.5%. I wouldn't call that "not sizable".
$7000 for five years of unlimited access to californian roadways and vehicle infrastructure? Ignoring the damage done to the environment and community health, the state is on the hook for $70b in maintenance in the same amount of time. So no, not really