I would like to purchase an inexpensive 3D Printer Kit to construct with my

I would like to purchase an inexpensive 3D Printer Kit to construct with my students . Can anyone guide me to the best source?
http://m.huffpost.com/us/entry/3518729?utm_hp_ref=tw

@Loren_Brandenburg thank you for sharing this amazing resource!

I would suggest http://printrbot.com, all their models are the cheapest on the market. But be aware that they are not complex enough for several persons to assemble together. You could buy several kits and have teams compete.