Low Cost DC motor Controler?

I want to power a 90 Volt, 5amp Perment Brush type DC Gear Motor. The, "Variable speed controller", needs to be able to use 115v AC or 115v DC input power, which is selectable by the operator. I have used a Staco variable tranformer which uses 115v AC input and rectified the output to drive the motor. But also need the 115v DC input option.

What is "low cost" here ?