You were paying the rate your insurance provider negotiated out of pocket. Again, all the pricing of healthcare is written up as if it were coming out of the health insurance company's pockets instead of yours.

In the midst of your one single incident, no, you would not have been able to negotiate the price of your vicodin. However, two things would change. First, they would not have offered you the vicodin without clearly informing you of the price if the norm was people paying out of pocket for most care. Second, if they charged $1k for vicodin but the urgent care down the street only charged $500, then basically no one is going to the first location. Rinse, repeat, until the prices are rational. So the cumulative effect of everyone paying out of their own pocket for most care is market-wide lower negotiated prices.