I was initially quoted a diagnostic on my vehicle and informed that the Injectors needed to be replaced

I was initially quoted a diagnostic on my vehicle and informed that the Injectors needed to be replaced. Then the following day I was informed that it is not the Injectors but Relays and I have to make payment in that regard. I was surprised when I when to make a payment of R1270.00... I was quoted R18000.00. Now it is as if the whole vehicle engine must be changed. I do not know how a diagnostic works.