Cheapest way of getting 2% ketoconazole cream in the United States?

I've been using a topical 2% ketoconazole cream to manage the sebderm on my face for many years now. It works like a charm (as long as I'm consistent about it), and it's OTC in Europe. But it needs a doctor's prescription in the United States.

What's the cheapest way of getting my hands on a few tubes? I'm almost out of my stock.