Wai = a happy cheer, yay (the ~ indicates a singsong extension of the vowel)
not for sale or rent - a common disclaimer on fansubbed anime
In the original version of this strip, before it was reexported in January 2002, the third panel had them labeled "Largo Usagi" amd "Piro Oniisan".
Usagi = rabbit
Oniisan = older brother
cosplay = costume play, dressing like an anime character
Piro's rant explains the overall reference to Nadesico.