Pharmacy Prescription and variable cost using insurance versus paying without insurance

TLDR; Pharmacy prescription is cheaper at local pharmacy without insurance than with insurance. Same drug.

I went to the doctor today and was prescribed a medicine. I have heard about Mark Cubans cost plus prescription company and wanted to compare prices. I called my local pharmacy and asked for a price on XXXX drug. She asked if I was paying with my insurance or a cash only. At the time I did not think my health care plan had a prescription plan with it so I said cash. I was quoted $50 for the generic version of the drug. The cost of the same drug at the Mark Cuban pharmacy was $30 plus $5 shipping. I was debating in my head if I should try it and wait a couple days for the drug or just go to the local pharmacy.

A little while later I get a call from the pharmacy because my doctor sent over the prescription. The lady on the phone informed me that my insurance (Aetna) didn't cover much of the cost of the drug and that my part of the fee would be $120. I told her that I just called a little while ago and was quoted a cash price of $50, how is it possible that through insurance my part is $120. She didn't give me a clear answer but said something to the effect that the insurance companies will raise the price of the drug to help get to pay the deductible faster for the customer. This is dumb logic to me because I don't go to the doctor often and I am on a very high deductible plan. The other part that stands out is that the lady on the phone said "Insurance didn't pay as much as they expected so my part is $120". Well how much did they pay, what is the actual cost under insurance?

Is this legal? It feels illegal. If it is who would I report this to?

I am going to try the Mark Cuban Cost Plus Pharmacy because the medication can be started at anytime. Also, my pharmacy has rubbed me the wrong way and I don't particularly feel like supporting them.