That is a question I was asked by one of my patients.  She just had picked up her antibiotic and had to pay $84 for it since that particular antibiotic was not part of her insurance formulary.  She then called me in couple of hours with so much disappointment asking why did we not check for her insurance formulary before we dispensed her medicine. 

The matter of the fact is, your doctor usually does not know whether the medication he is prescribing is covered by your insurance or not.  Your pharmacist does not know that either until he types your prescription and submits it to your insurance.  At that time, he gets prompted if your medicine is not covered.  If you are patient enough to wait for your pharmacist to enter your prescription before you leave the pharmacy, you get informed of your out of pocket cost.  At that point, you could decide whether you want to pay or ask your pharmacist to call your doctor for changing it to something cheaper.  Your doctor however, may refuse to change your medicine, since to his medical judgment nothing else would be as effective, or he may not mind changing it to something cheaper. 

If you leave the pharmacy before obtaining the price of your prescription though, you may end up with lots of disappointment.  By the time you come back to pick up your prescription, the doctor's office may already be closed leaving you no choice but paying a fortune.  You need to consider that due to heavy volume and your pharmacy's time constraints, it is really not practical for the pharmacist to call every single patient whose medication is not covered.  Plus, many patients decide to pay out pf pocket for the uncovered medicine anyway. 

The bottom line is, if money is an issue, and you don't want to end up paying a fortune for your medicine, ask your pharmacist to enter your prescription before you leave the pharmacy.  You could also call your pharmacy in half an hour to inquire about the price.  That way, you leave yourself with enough time to have your doctor contacted in case your medicine is not part of your formulary. 

Good luck, and be well.