The modular ones are the best , but you get a very cheap aluminium extrusion called “ticket rail” that takes slide in 2mm or thinner sbstrates plates , you can cut these to any length and they generally come in 1″ , 2″ , 3″ and 4″ widths. I think this stuff costs us about 10 quid for 6 meters of 2″.
We stick these extrusions in rows on an acrylic or wodden backs and use side pieces we cut to suit (that are attached with small grub screws to the back board to make then mremovable to change the inserts) to close the ends when we have put in our slide in sections (you can make these slide ins with aluminium and vinyl letters ,engraved plastics , encapsulated digital prints etc and if you make em of fflexible stuff and a little wider than the channel , they bulge outward for a convex effect.
Problem with these jobs is that you do the big board at a decent price etc , but then you get calls for one plate which are generally a pain in the butt , so maintaining them becomes a schlep:)