One of the popular places to get Viagra, etc.
Currently 1,500 yen per 50mg tablet ($14 USD) for the real Viagra. Cheaper versions are about $8 USD per 50mg tab.
You can legally order it online through some offshore Japanese sites.
The generic for Viagra is about $13.60 per 100mg tablet. (or $5.20 each for a cheaper brand)
Cheapest I see is ~$4.70 per tablet (50mg)