I use the iPod touch's price and go from there.
I respect the idea of thinking of it as a super "touch" vs. a super "phone", but then this super mobile device won't have always-on access to the web. That makes it a lot less usable from a mobile device point of view, as it would then be tied to wifi (hopefully wimax) sources, rather than getting what you need to know from it, whenever you need to know it.
If it is competing with devices like Kindle, it needs to match that device's ability to get content via 3G from anywhere at anytime. However, if it is going to "fit" into the Touch/Phone lineup of Apple products, it will need to be more than just a Kindle (more than just a 3G only to buy stuff function), as mobile Safari seems like a feature that will heavily differentiate it from Kindle and Kindle-like devices. How do you get mobile anywhere without 3G?
If it is competing with netbooks, it needs to do a pretty good job against all that a small laptop can do. Since we know Apple won't compete on price, it is going to need to do a bit more than what those devices can do. Again, an always connected 3G source contributes to justifying a higher (Apple) price.
And before someone pitches 3G data only at some super low monthly rate, note that any 3G option gives this full mobile phone capabilities- be that through standard voice 3G or through mobile VOIP. A lower priced- but full 3G connection would become the cheapest option for anyone who needs mobile phone communications.
For myself, I really hope it is more iPhone than Touch, as I think that's the major draw (for me)- I don't have an iPhone. If it comes with the mobile connected limitations of the Touch, why not just buy the smaller Touch?
And I still believe the 3G subsidy model is how we get the "shockingly low price." I can't imagine all this hype and "gee whiz" buildup for something Apple launches at $299-$499 or so in 2010 (without AT&T or Verizon, etc chipping in on the rest of the TOTAL amount Apple wants for this thing).