I have the vinyl roll-ups on both my trucks. Only because of what I do. A complete interior out of a vehicle doesn't fit under a closed hard cover, especially in a short box. So mine tend to be on & off a fair amount. I can't remove a hard cover by myself.
For my '98, I bought a tonneau for a long box off of C/L for $100.00. Took about an hour to shorten the frame & the vinyl to fit the short box. Any upholstery guy that even sorta knows his stuff should be able to do the same. You could mod the frame, then take the truck to the stitcher for him to mod the cover. If he wants to charge you any more than $50.00, your being robbed!
For a step side, the vinyl would also have to be narrowed. Even if you came across one with a good frame, but the vinyl is trashed, it really easy to make up a new one. But the key is to have the frame. That way the tonneau is attached to the framework, which is held onto the truck via clamps.
I've made tonneaus the old school way, without the frame. The attachment snaps are installed directly onto the trucks box. But I don't like to do this. For one, I hate drilling holes in a customer's vehicle, (long story, lesson learned!) & all the holes drilled for the snaps are just one more way for rust to get a foothold.