Is it permissible for me to purchase a car designated for people with disabilities, the price of which I pay, and then have the person with disabilities, who cannot afford its price, sell it to me, knowing that it is his right?

The questioner is the real buyer of the car, and the disabled person is merely a means to evade customs. If customs duties are something the state has the right to impose, then it is not permissible to evade them. However, if they are unjust taxes, then there is no objection to evading them and using the aforementioned means to avoid paying them.