How does one find out the true cost of medicines?

I just had two prescriptions filled. One was for fluticasone steroidal creme filled as a generic. This one cost me $3.00 and the other was for Omnicef which is an antibiotic. That cost me $10.00 because there was no generic available.

I’m just curious how much this would have cost if I didn’t have insurance.

It depends on what drugstore you go to, for one example here a partial price list from CVS Pharmacy. Sometimes it is also noted on the prescription bottle or you should be able to ask your pharmacist.

Walgreens has a pretty complete list.
That Omnicef looks pretty expensive. Now don’t forget, the prices you see on the Walgreens site are the prices for people with no insurance (which is what you asked for), but even if you have a high deductible plan and are still paying out of pocket, you’ll get charged the discounted price your insurance company would get charged.