Between the Brooklyn, NY; Paterson, NJ; and near Philadelphia, PA; MicroCenters there are more than merely those AndyMark parts. Course the cheapest tax is NJ where it is merely 3.5% because of the redevelopment zone (same for Lowes across the parking lot). So score for the rest of the robot materials
. MicroCenter also sells 3D printing goods so there is another bonus (Inland ABS/PLA works fine in my RepRaps).
They have some wheels and some gear boxes but you really have to look in Paterson because that store is always disorganized.