Computer power supplies cost around US$30, much cheaper than lab power supplies! By converting the cheap (free) ATX power supplies that can be found in any discarded computer, you can get a phenomenal lab power supply with huge current outputs, short circuit protection, and reasonably tight voltage regulation on the 5V line.
On most power supply units (PSUs), the other lines are unregulated.
WARNING: OPENING A POWER SUPPLY CAN KILL YOU. USE EXTREME CAUTION INSIDE THE CASE. THE CAPACITORS TYPICALLY STORE 300 VOLTS DC. AVOID TOUCHING IN ANY WAY!