Here's my logic:
Apple, just like most other companies, seems to spread its products out over price points. For example, the ipod prices are 69, 99, 149, 199, 249, 299, and 399. With the current MacBooks, Apple does not have anything under the $1999 mark. To my way of thinking, Apple will need to spread out its products over this price range, which means we can expect portables at least at about $1499 and $999, and probably lower and higher. Given Apple's iPod success at the low end, they might want to offer iBooks at prices lower than $999.
My point is that Apple has plenty of price point room to offer anything it wants among what people are guessing, so right now, we don't have enough information to make very informed guesses. What we do know is that just about anything is possible, including a 13" MacBook Pro with a 2 Ghz processor and a $1799 price point, or an iBook with the cheapest single core chip, 40 gb HD, CDRW-DVD drive for $799. Keep in mind that it would still be faster than the current iBook on UB apps.