I cannot give you a price on 2 1/2" reloads but my 2 3/4" using 3/4 oz. was below $4.00. That is using Red Dot(at the time, Claybuster wads and Eagle Brand shot. This was a few years ago when reloading prices were not as high as now.
I use 12 ga. 2 1/2" hulls for my vintage 1892 Greener. I cut the shells in my drill press using a dowel turned down to fit inside the hull and set the height next to a block holding a box cutter, push the cutter against the hull and it parts it smoothly.
This picture shows me cutting 20 gauge hulls to 2 1/2".
I roll crimp the 12 gauges with an old hand roll crimper, I find it faster than the one in the drill press.
These are 16 gauge done in the drill press using 2 1/2" 16 ga. Cheddites (bought)
As to using a spacer, I made one out of 1/4" aluminum and put it underneath my 600 Jr.