Not to refute some of the good advice here about suspicious, cheap, online sources.
I was referred to, and use
www.4rx.com
100 mg tablets are about $2.50 each, (40 for $89) with shipping. Tadafil (the actual drug compound name.
One hassle, maybe.... they require Visa only. NO Amex or M/C. Shipping takes about 4-5 weeks, but is reliable. Arrives in a plain envelope with no special marking at all.
I know some of you fellas are gonna go " Oh yeah, BUT...." That's fine, I'm just giving you some personal experience with this outfit. I was referred to them by a close friend that has used them for quite a while with good results. Free info.. no refunds of $ paid for the advice.