You can buy a lot of things black market, but it doesn't mean you should. United Health Care is my insurance and it used to be $5 until I switched to a different plan. I had Cigna before that and it was $5 as well.
Also, if a vial is only lasting you less than or barely 2 months, that is going to be a red flag for any insurance because that is a high TRT dose. Cigna and UHC won't do anything under every 3 months.