Old desktop computers are thrown into the trash by the thousands. You can salvage a power supply from one, or buy new at a computer store for under $20. Then follow these instructions to convert to a very respectable high power benchtop supply. Follow all safety precautions!
Detailed information and how-to: http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply