As a reminder, a Raspberry Pi is a single board computer, small as a credit card, having an 700 Mhz ARM processor, 256 Mb of RAM (Model A) and 512 MB of RAM (Model B), an ethernet port, an HDMI port and 2 USB 2.0 ports. Pluged in at a TV / Monitor, and with a keyboard and mouse added, it is a modest Linux computer.
NOOBS (New Out Of the Box Software) is an installation system for Raspberry Pi allows its users to easily install different operating systems on their single board computers.
To my mind, 5$ for an 8 GB SD card is a good price. It’s like, you donate 5$ to the Raspberry Pi developers, in order to support the RasPi project and get an 8 GB SD card as a gift.
The NOOBS installer can also be downloaded from the official Raspberry Pi site.