Paying R720 for quote

I took my car to Gobies' this morning after I've learned that my alternator is overcharging. The guy told me he is guessing that it will not be more than R800. They phoned me now and told me that they can not fix my alternator I have to replace it, which will cost me R2900, which I don't have, and that I have to pay for the labour, even though my car is not fixed at all. So I am basically throwing this money in the water, which I can not afford to do! I asked them if I happen to find the money for the alternator, if I will again be paying this fee, and the answer is yes. I think it is very expensive and overcharged. I can understand it took them time, but I've specifically told the guy I do not have a lot of money. Surely if they can't fix my car, they have to also accommodate the client in some way?