When you're in your doctor's office and discussing the tests they want to order you're very unlikely to be able to get the cost right there during your appointment.

You would probably need to have the doctor print you a list and then after the appointment contact the hospital/provider to find out... which could be a huge delay in getting the tests done and involve a lot of extra travel time. And I can only imagine the effort required to shop around for the cheapest place to have your blood drawn that also orders from the cheapest lab for whatever tests and that also takes your insurance.

The best I get is my PCP will be like "I want to do this test for this reason but it is usually more expensive so I won't order it if you're worried about cost".