There is no supply side reason for the high price Mylan is charging for EpiPens. It is a couple bucks worth of materials (plus QA, distribution, and all that). The R&D costs have long since been amortized away to nothing.
How do you know? The medical industry regularly has shortages of dozens of different products [1]. And that is to say nothing of the cost of navigating through all the regulatory hurdles.
The price of epinephrine in other packaging (vials, ampules, etc) has remained more or less unchanged (speaking from firsthand experience as someone who orders supplies for an ambulance service). It is not an epinephrine shortage driving this price increase.
Similarly, the EpiPen is already an FDA approved product, and has had no new regulatory hurdles to jump through recently.
[1] http://www.economicpolicyjournal.com/2015/10/drug-shortages-...