If you want to consider buying before you fly, i got this viagra clones link off another forum, although i have never personally ordered from this site, i intend to before my next visit to Phuket, so don't shoot the messenger if any probs.
I have tried Caverta from another source and can vouch that for me it was just as good as viagra.
If my maths are correct you can purchase from as little as 69 Baht each excluding postage, if you split in half better still.
If you have any Indian friends ask them to bring you some back next time they visit home, apparently it is dirt cheap in India, one guy i know brought lots back and was handing them out at work like they were sweets, he's now one heck of a popular guy.
http://www.genegra.com/order.htm