Over Instructables there is a how-to on making a laser cutter for less than 50 bucks.

A video showing the basic setup:

Here’s the list of materials you need:
1x Laser diodes Ebay Store $36 dollars for 2
2x Old Scanners Salvation Army $10 Dollars each
2x ULN2003 Electronic Connection $5
1x Prototyping board RadioSchack $2
2x 3/8″ Aluminum Rod Home Depot $3 each
1x 3/8″ Aluminum Tube Home Depot $3
10x Brass Brackets Home Depot $1
1x 2″ cube of wood Home Depot $1
A bushel of Patience

Following is a video showing all the supplies you’ll need including the tools: