Charles K :
I used to run a 1' x 4' switching layout with a secondhand Mantua Booster. It worked well, and was about $10 at a train show. One motor brush is grounded to the chassis; to DCC it, slip a piece of electrical insulation over the retainer spring and add another feeder wire. This goes for most open-frame motors. Model Power is now selling the similar Mantua saddle-tank 0-6-0T which is simply a Booster with an added axle.
Some recent experiments I've done with a Life-Like Teakettle have convinced me that this engine and their Docksider with a similar drive can run excellently if remotored.
Older Mantua/Tyco 'Plymouth' switchers are plentiful and cheap - $5 at hobby shows is typical - and the MU-2 truck can be made to run pretty well.
The newer Bachmann 'Plymouth' six wheel diesel was shown to me at a model shop, and appears to run quite smoothly and slowly.
Model Power has two 4-wheel diesel switchers and an 0-4-0T. I don't know how well or badly these run. Bowser also has a B&O 'Dockside' 0-4-0T. Again, I don't know how it runs, but it has a can motor and a reasonably good mechanism; probably it's okay.
If you can find one (I can't) the MDC boxcab or Climax are said to be noisy but slow and strong runners. They are quite small locos. MDC also made an 0-6-0T kit.
The nice thing about these small switchers is that they don't take up much space...and space is what you don' t have much of.
Cordially yours: Gerard P.