What is the simplest way to control a motor's speed

I have a couple of boxes of stepper motors mostly salvaged from old
printers and copiers. I also have a few small 5-24V DC motors laying
around. Eventually, I'm going to build myself a small CNC machine,
but until I have time and resources my current project seems fairly
simple. I need to control a motors speed over a range of 0 to near
100% with a potentiometer. I don't care anything about reversing it,
what it's position is, or if it is a stepper or dc or RC servo. I
would prefer the cheapest and simplest way out. I have found tons of
stuff on the net, but everything seems to be oriented around a
microcontroller or PC control and all I want is a simple speed
control. Can someone give me a suggestion on where to look for a
prebuilt solution or a decent kit?

Thanks,
Doug Nicholson