Have you never looked at an itemized medical bill? This is exactly how all medical practitioners in the US that accept insurance do things.

Every procedure, every Tylenol, every operating kit has a code and a price and that is all itemized and billed.

Try calling up your mechanic and asking for a quote. Tell them your car is not working right and you don't know what's wrong, but you want a quote before bringing the car in.

Now, if you call a medical practitioners and tell them exactly what tests or procedures you want, they can probably look that up for you.