> Mark Cuban's pharmacy, however, refuses to deal with your insurance

I don't see a problem with this. Some insurance plans are can be hard to deal with. My personal experiences involve requiring step therapy (trying a cheaper, possibly less effective drug) before approving the prescription. Another experience is that a drug may only be covered for one condition but not for another (e.g. finasteride for hair loss vs finasteride for enlarged prostate).

If Cuban wants to avoid the headache of dealing with formulary lists, I don't blame him. Obviously consumers should compare prices whenever possible, but if the difference is only a few dollars I'd probably rather pay Cuban directly than deal with the Walmart retail experience.