Starter Motor

Hi I have a renault clio 1992 J reg automatic 1.4 Rt car and my starter motor is playing up. I have to wack it with a hammer then it will start but as soon as I turn the car off it wont start without me having to hit it again. Now this time last year I called the rac out and he hit the motor and its worked ever since about a year, so do I need to buy a new one? Or just take it in to a garage for expection? Or will they try and rip me off and say I need a new one as I have called a few garages and they have said it's going to cost alot as they have to remove the drive shaft. Please help!