Sure, you can buy a foam cutter, but wouldn’t it be much more satisfying to build your own? MAKE author Bob Knetzger–who wrote this great Desktop Foundry project, shows how to built a foam-cutting rig with a length of nichrome wire (similar to the elements you gave in your toaster) and a model train transformer.
It turns out a transformer is ideal for controlling the hot wire. Not only does it deliver the amps you need (divide the volts by the nichrome wire’s resistance to get amperage; OHAI Ohm’s Law!) but they typically have a speed controller (potentiometer) allowing you to adjust the temperature of your cutting rig based on the materials you’re working with.