Can you just keep going through the grants process see what they offer, then use any ap they will give to order what your son needs and you are happy driving, you only need to get the dealers letter which states the amount they will give, it doesn’t state that you have to spend it on the vehicle they say, you will just be liable for the rest of the ap, see what vehicles they say but you should get a range from what to choose from it won’t be one specific vehicle.