[techhelpbb]

Do you want repeatable cheap or coincidental cheap?

I got a bunch of AndyMark ToughBoxes from MicroCenter on triple discount - that's coincidental cheap.
I got a bunch of Grayhill encoders cheap from a surplus shop - that's coincidental cheap.

Then there is cutting corners on the frame cost and just slapping on some inexpensive motors.

You certainly can scale down a FRC style robot. I have a test frame I fit into a largest hard shell suitcase you can carry on a plane. You put the battery, laptop, and charger elsewhere. It fits in the back of my 2005 Honda Insight Hybrid Coupe over the electric motor and batteries (the car is considered sub-mini) and as that back is a hatch I can lift it out myself (I am a 6'3" 280lbs male and the case has swivel wheels with retractable handle, which came from Walmart).

Stacked plate drive train can be made with a simple drill press and Forstner bits with some care. Stack them with spacers made of pipe or whatever you've got handy. Use cheap threaded rod and some Loctite to save some cash on hardware. Worst case for wheel hubs pour some Shapelock/Polymorph in the hub and mold to need, locate center with a jig or lawnmower blade balancer before you start. If you have a Tractor Supply nearby they usually carry cheap bearings. Should be able to cut the aluminum plate to shape on a table saw and/or a miter saw. Could even do this with wood: just remember that wood changes dimension with the seasons (and lesser grades of plywood have voids inside the layers) so use a decent grade of plywood or even aircraft rated wood. Might look at steel tubing in the auto part store for the spacers.