While I wasn’t paying attention, ultra-low-cost, ultra-mobile computers have become serious competitors in the mobile device category. Over the next few days, I’m going to look at some of the contenders in this space available through PriceGrabber.

I’ve already written about the Asus Eee PC, which became quite popular after the One Laptop Per Child program was introduced for international consumption. The idea is to put a low-cost, low-power connected laptop into the hands of children in the world’s poorest areas. But the idea that you could have a computer that weighed in at three pounds or less and that cost under $600 was truly appealing to a lot of technology users, not just the people in developing nations. So other companies — including Asus — have arrived on the seen to fill the perceived need.

To keep the costs down, the companies involved in selling to this movement have often gone with legacy or open source operating systems, such as Windows XP or Linux, and kept hardware options to a minimum. Some computers include no CD or DVD drive; others have solid state drives, but no hard drives; the processor doesn’t have the fastest clock speed on the block. At each step the expense has been shaved in creative ways. Expectations from some companies are that you’ll do your computing “in the clouds,” relying on free services from Google and a hundred other dot-com companies to give you productivity applications and maintain your data.

Also, a lot of the devices include small displays (seven or eight inches in size) and smaller-than-usual keyboards, intended for the small hands of school kids. On the plus side, many of these units are built with extra durability. If you drop them, they may bounce but otherwise work fine. On the minus side, if you have sausage fingers or poor vision, you may find yourself struggling to type or read what’s on the screen.

Yet when you only spend $300 for a computer, you could almost call them “disposable.” Your expectations can be lower, because you don’t have as much invested.

So, coming up, rundowns on the HP Mini-Note PC, the Everex CloudBook, the Acer Aspire, the Lenova ThinkPad X300, and the Sony VAIO VGN-TZ210E/P notebook (not cheap by any means, but wonderfully small and packed).