Idk how hard this would be code with your system but I think it would be a very popular gold perk and even encourage players that don't have them to buy the existing "sell unlocked..." perks s well.
The idea is to have a perk that creates a second lock button next to the existing one for items that EITHER locks a static % of your inventory of that item (like 50%) OR to have a setting in options like with the large net launcher that lets the player set the % that locks for all items this button is used for.
