I mentioned the drill idea because 1/4" variable speed drill probably operates at the speed you quoted. Also the power output is about 1/4 HP. The AC plug in the wall version is most likely the cheapest motor you could get. But mounting and the fact that you have to plug it into the wall doesn't make it very portable. The portable battery pack versions don't have the speed or power output. Check out an example here: Makita Drill
The RC motors I used in my Zero Time Generator are Tamiya Super Stock RZ. Super Stock RZ
But fabricating the gear train to gear it down along with a speed controller will definitely increase the cost. But then I got a couple of horsepower per motor with my design. And then this design fit very well with using a 12 volt car battery for the power supply. These motors are the brush type motors. The newer brush-less design is very expensive to use. I haven't researched those yet. Also I fabricated my own pulse width modulated speed controller. I built the controller to handle up to 300 amps in case of stall conditions. If you decide to go this route I could whip up a circuit diagram for the controller.
Your engineering abilities remind me of Eric Dollard, who iam sure you know a little about

As you obviously know, Dollard is from the "old school" of electrical engineering

