It's always a matter of scale, if you're only looking at a few dozen to start off with then, assuming that you are looking at about 31/2" x 2" plates, you could probably do a trial batch by hand cutting the plates from washed (empty) bean tins using a pair of tin snips (get yourself some heavy duty leather gloves to protect your hands), file the edges to lose the sharp bits and then epoxy glue the bases to the frames. It would work as a proof of concept and isn't that much of a pain once you're used to it
Edit - It's possible that you have a steel stockist locally (most cities will have at least one) who might be able to supply thin gauge steel sheet in small quantities which will cut down on the work you have to do.
Edit 2 - If you do go to a steel stockist that has a front desk, don't go at brew time! You're likely only looking at spending a couple of dollars and if the stock is at the far end of the warehouse.....
Edit 3 - If you can find anywhere that's hack sawing/band sawing a lot of steel then they'll be creating a lot of steel 'dust' (bench grinding would probs have enough iron content in the dust as well) which could be mixed with any paint that will stick and then painted over plasticard or whatever else - possibly just poured into the wells of the tray and left to set (do this on a polythene bag or sellotape that can be peeled off the back).
OR, BETTER YET, SEE NEXT POST