You can see a pic of my livewell, it was very easy to make and the most expensive thing was the bag at about $5. I have several of these that I lend to friends when we go tubing.

http://photos.yahoo.com/bc/mywoodsac/vwp?.dir=/Float+Tube&.src=ph&.dnm=0929009.jpg&.view=t&.done=http%3a//photos.yahoo.com/bc/mywoodsac/lst%3f%26.dir=/Float%2bTube%26.src=ph%26.view=t