Right about $50 when you buy the dohickey from him and order the yellow temp device off of ebay:
If you are not familiar with Russ and his videos:
https://www.youtube.com/user/SarbarMultimedia/videos
If you want a tighter/more distilled set of videos from him, view the ones he made for ThinkLaser. You just want to view the "How to use a laser cutter" ones.
https://www.youtube.com/channel/UCt0...FJRBdfA/videos