Sony swivel NR-70 is $500 USD
For more, you can check out sites like PalmInfocenter.com. It's more expensive here (US) than in Asia.
It's currently the fastest PalmOS device (66 MHz 680xx Dragonball). For anything faster than that, you'll have to wait for ARM-based Palm 5 based machines in the fall. Other downsides include low battery life (half that of the T615) and larger size.
The Zaurus is available at Fry's, but it's a little pricey (similar to PocketPC, about $650 IIRC). Next time I'm at Fry's I'll have to look at it in a little more detail.
BTW, you can also run Inferno OS on iPaq's -- I've seen it done at trade shows.
And, I'm very happy with my new Sony T615 (blue). Then again, I only want a PDA, not a singing, dancing, mainframe that finds in my hand.
Tony