One could also just make the base rate $150/day and then you'll definitely make it untenable for as many people as possible, which is apparently the goal. This leads to an outcome which is you think is an unfair distribution. But luxuries are necessarily for those who can afford them.

The 'cost' of the action is the same. A vehicle in the city is a vehicle is a vehicle and therefore the toll should be flat, unless that type of vehicle in particular causes more damage to roads or empirically worsens outcomes like traffic or pollution relative to other types of vehicle. Charging people more because they are wealthier is unfairly discriminatory.