Always tell them you are paying in cash. Take bill home and sumbit to insurance if you are lucky enough to have insurance. You just saved the system at least 75% of the cost.
One of the weird things going on right now is that Doxycycline (a common antibiotic) has gone up in price 10-20x in the past couple months. A bottle which used to cost me $12 generic is now...$350! (due to a crazy FDA recertification process for the manufacturers)
My local pharmacist laid in a huge supply at the old price, and when I told him I was on an HSA (and where he saw my insurance deductible of around $250), he sold me the prescription for cash for $30.
Still covered for anything serious (essentially any ER visit, cancer, serious illness, imaging, etc.), but for anything else, I'm highly incented to negotiate like I would for any other product. Best of both worlds.