The Raspberry Pi Model B is one of the cheapest $35 Linux mini computers for the Model B version which I ever own. The reason that the Raspberry Pi is so cheap is because it uses mobile parts, and because of its small size.
The Raspberry Pi is cheap, and small, but it can do many desktop tasks like surf the web, programming, office work, and playing games like Minecraft PE Pi Edition, Quake 3, and other games. It can even play video with OMXplayer, or with Rasbmc, or OpenElec which are Multimedia operating systems for the Pi which has the popular XBMC media player installed on it.
The Raspberry Pi mains operating system is Rasbian which is based on Debian which is one of the most popular Linux operating systems.Rasbian comes with programs like Scratch, and Python which you can use to learn how to code programs on. Rasbian also comes with a web browser, and the Pi App store for downloading, and installing programs onto Rasbian.
I mainly have been using my Pi to play games like Quake 3, OpenArena, and Minecraft PE Pi Edition. There are about 40 games available for the Pi in the Pi App Store in Rasbian. The Pi is also good for playing video, music, and viewing with Rasbmc, or OpenElec. It can play HD video pretty good in my experience. Web Browsing on the Pi is slower, but it loads more basic sites like Craigslist pretty quickly.
The Raspberry Pi also does not use much power because it uses a MicroUSB charger as its power source, and the Pi is very power efficient because it only has 512 MB of RAM, a 700MHz Mobile CPU, and uses a SD card for storing the operating system, and files. All the parts on the Pi, and the SD card uses very little power because there are no moving parts, and the Pi does not need an electric fan to cool it like other computers like desktops, or laptops. The low power usage of the Pi would make it a good computer for displaying pictures and video on a TV or monitor, using to play music by plugging in a pair of speakers, and using as a file server. I also seen videos online of people using the Pi to make a mini laptop, and tablet with a small screen, keyboard, and battery pack to power the Pi.
The Pi is also noiseless, and does not generate any noise because it does not have active cooling fans, or a spinning hard drive like a regular computer which needs spinning cooling fans to cool it, and uses a hard drive to store the operating system, and files.
The Raspberry Pi is an affordable, small, and quiet computer which is great for learning how to use Linux, coding programs, watching videos, listening to music, and light web browsing, and office work.
I recommend buying or making a Raspberry Pi Case for the Pi to protect it from dust, damage, and dirt which may damage the Circuit board. A Case also makes the Pi look cooler and more unique.