Make your own liquid nitrogen for under $500 Answered
Ben Krasnow built a machine that makes liquid nitrogen for under $500. It's made with many parts he bought off of eBay and can generate a liter a day of the stuff at a cost of $1.15 per liter. Check out the link for more info.
The first video is from this year's Maker Faire and the second shows the effect of liquid oxygen on a BBQ.