It used to be that the worth of a book was measured by what the reader could carry away from it. Now, it seems, worth is being measured in how the books are actually carried. And what that’s worth has started a war – the price war of the e-readers.

Barnes & Noble reduced the price of its Nook e-reader from $259 to $199 this week and also said that they would release a lower-priced, WiFi-only version for $149, making it the first under-$200, full-featured e-reader that offers free 3G and WiFi connectivity. Not to be undersold, Amazon cut Kindle prices by 30%, from $259 to $189.

As to others in the e-book reader marketplace, the Sony Pocket Edition is priced at $169 with no wireless connection, but their Daily Edition does have Internet access, but that costs $349. At least until Sony announces a price cut. Borders offers up the Kobo. It’s $150, but it lacks wireless access too.

Amazon was, of course, the early leader in the small but growing market for portable reading devices. Now they’re facing growing competition with Apple's iPad, Sony's Reader, and an array of other handheld tablets and mobile devices. The escalating price war reflects the growing popularity of e-readers as well as Amazon’s and Barnes & Noble's desire to offer a lower-priced alternative to the Apple iPad. That retails beginning at $499 but does other things besides holding e-books.

But all e-book readers are not the same, having different e-book formats. Apple and Amazon don’t allow other manufacturers to use their copy protected e-book formats, but Barnes & Noble's ePub is available on different devices, including Sony's e-reader and Borders' Kobo. And as to who’ll be left, at least one e-reader maker has only made it to Chapter 11. IRex Technologies recently sought bankruptcy protection. Other brands, like Plastic Logic, have encountered delays as well entering the growing marketplace.

The advent of multi-featured tablet devices and “MID” devices (mobile Internet devices), aka “tweeners,” or something ‘between technologies,’ has driven the prices for single-feature devices lower and lower and lower. Amazon and Barnes & Noble are expected to introduce new models as early as this summer, which means prices of e-readers are likely to come down even further. One industry expert thought that most devices would end up being priced around $100 by the end of the year.

The e-book reader price war is far from over, so stay tuned. Because this marketing and technology war is bound to turn into a real page-turner!