Ins. companies don't technically buy drugs, they utilize a pharmacy benefit manager as a middle-man to service their prescription benefit plan- unless they're big enough to have their own PBM company, such as Aetna.
People 65 and over receive Medicare, before a person turns 65 they will receive paperwork instructing what to do. You can supplement your Medicare with AARP -you can get AARP at age 55. AARP has several supplemental plans to choose from, I was looking over my Mother's paperwork from AARP and the lowest plan will cover your Medicare A hospital deductible and nothing else, I believe that was under $100 per month, and then the highest coverage plan that takes care of any out of pocket costs after Medicare pays was about $200 or so per month.
If you're under 65 and have to pay for private insurance- the costs are prohibitive to have an individual insurance policy.