I've thought of doing this in the past, but I'd have to charge like $5 per 100mg pill to make it worth my time. Plus I'm too damn busy anyway. That's with "free" shipping on US l orders. I believe enough guys would be interested to make a little $$ with a Viagra biz.
With most if not all of the online sellers no longer taking card payments, many would buy to save on the shipping cost and 2-3 week wait as well as the insecurity of sending paper payments in the mail or having to use bank transfers.
Hint hint somebody looking to start a biz, hint hint. You'd need a PayPal amount to take card payments. You'd pay about $1.37 per 100mg pill with a profit of $2.50 ish a pill. You'd be smart to only accept a minimum order of $30-$40 which most guys could handle. Sell the value of the 100mg pill as two 50mg doses.
Hell you'd not even need a site to start if you did it right. PE forums and body building forums would be a good word of mouth start.