Well, the Pismo was the first G3 to use the originally designed Apple Airport card, so the Apple Airport Extreme card could work, though I haven't tried it myself yet. Anyone with experience on this issue, please post.
The Airport Extreme card will not fit into a Pismo. The original Airport card is based on the traditional PC card form factor. There are several manufacturers of Airport Extreme PC Cards for the Pismo. Asante, Buffalo technologies, sonnet Technologies, Orinoco, Belkin, and Linksys are all vendors that manufacture these cards.
The price varies from about $60-$100 for the card. Then you're looking at another $200 for the Airport Extreme Base station.