This diy foam cutter is relatively cheap and the results are quite impressive.
HOW TO - Make a hot wire foam cutter - Make
4-Axis CNC Hot-wire Foam Cutter (Arduino+Ramps1.4) : 9 Steps (with Pictures) - Instructables
4-Axis CNC Hot-wire Foam Cutter (Arduino+Ramps1.4) : 9 Steps (with Pictures) - Instructables
LowRider-inspired Foam Ripper - Things You've Made - V1 Engineering Forum
Make a CNC Hot Wire Foam Cutter From Parts Available at Your Local Hardware Store : 17 Steps (with Pictures) - Instructables
Building a Hot Wire Foam Cutter
Watch This 5-Axis Hot Wire Cut Beautiful Foam Shapes
Building A Four Axis Foam Cutter From Hardware Store Parts - Make
Make Your Own Four-Axis CNC Foam Cutter on the Cheap
Arduino CNC Foam Cutting Machine - How To Mechatronics
Arduino CNC Machine Foam Cutting