But there is an ultra low cost (~$10) robot kit in the works (trade-off of course being less features/usability), but it's not available yet: https://sites.google.com/site/affordableeducationrobot/home
At $99 is the Pi-Bot http://pi-bot.org/
$50 Hack-E-Bot http://www.hack-e-bot.com/
$100-$150 littleBits http://littlebits.cc/
$99-$250 Finch & Hummingbird http://www.birdbraintechnologies.com/
$250 Arduino Robot http://arduino.cc/en/Main/Robot
$100-$150 Parrot Minidrones http://www.parrot.com/usa/products/minidrones/
and many others