I would do vin check if you do not know the person, and see when the inj's were last changed. I buy and sell a few car's on the side. I would personally start at 6-6.5k$, and prorate the price for injector's. IE, I est. that inj's will last around 100,000mi, and the job costs about 3k. So say the vin check says they were changed at 250xxxmi, -1500$ + 6500$ = 5000$.