Do not feel limited by your gear of what you can deliver. Your creativity is your limit.
As for charges, what can you convince your buyer to pay?
As to your skills in setting up a rig for car shoot, your ability to shoot product, your understanding of shooting models, it is all your responsibility. There is no excuse when you dont do it well as a paid photographer.
I do find it hard to charge my relatives or good friends for services. Either i dont do it or its free for them. But if am doing it as a full time - ie shoot to feed - then it is only fair i be paid for time spent. It is called opportunity cost.
As a guide for commercial rates, it is usually determined by estimated number of hours. Multiply your hourly rate to get a gross figure. Some charge $20 per hour, some $200, some $500.... It's all up to you.
Also, do you have a contract drafted out since it is a commercial shoot? You need to be protected with terms and conditions (in your favor mostly) even if you were to charge $50 for the whole shoot.