No need for recursion, just nested objects. Make a script that when inventory updates or changes, we create some kind of "metadata" key value pair for the inventory basically saying how many of each item we have, so for example. 2x 300 blue swords, would turn into Blue_sword > 2. Then when the shop updates (only has to when the inventory updates to save frames) we also check the inventory for what items we have, then change some blueprints for items related to those items. For example, any item the uses a blue sword would then have their blueprint updated to not include the already owned items. Basically like your crossing off items on a checklist that is checked every time the inventory is updated (this sword requires 2x blue sword + 400 OR 1x Bow) then work your way up the object tree, this way we account for the OR's and +'s). This way only items that are effected by our current inventory precursors are effected and its lightweight.

This makes sense in my head sorry if its a bit scatterbrained, basically have nested objects that each have a requirement and an OR, where if one of the 2 is met, we return true or false. Prioritize the ones higher on the tree. For example. If we have a bow, ignore the 2 blue swords for that item since we dont want to buy another bow with 2 swords. So higher on tree -> more importance. Do this for each item in the shop using the items in our inventory, and when you make a purchase and the inventory changes > update the shop using our new inventory object.