Earlier in this thread I listed the bucket heat I use from Jeffers. It is important the element is cages so it doesn't hurt the plastic. I use a honeywell digital temperature controller I got from here:
http://www.northernbrewer.com/brewing/j ... oller.html
If you have a flat bottom kiddie pool, you can use a few water bed heaters. Just put them under the pool. This is a great low cost option as you can get 400 watt heaters on ebay for around $15.