Let's say you want a store to offer a 50% Discount even though the store is stocked with common items you can buy anywhere else without every store also offering said discount. This is do-able.

DATABASE
-In your Database, duplicate the items relevant and alter their Price so that you now have "Full Price Versions" and "Discount Price Versions."

EVENT (the shop clerk offering the discount)
-Make Variables for each Item.
-SET the value of each VARIABLE to the ITEM and Number Held.
-Remove "Full Price Versions" of each item by the respective Variable
-Add "Discount Price Versions" ...
-Call Shop, stocked with "Discount Price Versions"
-SET the values of the VARIABLES again.
-Now Remove "Discount Price Versions" ...
-Add "Full Price Versions" ...

This is a very inventive idea. You could take it a step further by keeping a global variable of over-produced items in certain regions and tying them into in-game events.
If a town is undergoing hardship, then potions would cost more. If you improve the town/region, then the prices of healing items will drop to accommodate the decrease in demand.

Of course, it gets a bit more complicated here, but still something for an 'open world' game to consider.

Thanks. I'm also considering an idea of International Trade where the price of goods can differ by region.

I have found a script of this somewhere, but yeah, im not here to ruin your work, and i praise you for finding a new way to do it, although i think it adds a lot more work for people who are using XAS or a lot of items like i did in my project, where i have to duplicate item (that is ok), but for weapons, i have to do a bit of scripting for it, by that i mean add it as a new weapon, and give it same properties and give it a new ID, not that it's too hard, but it just adds a bit of work.

I once again want to tell you that i'm not here to ruin your work, i just want to throw some extra information at it, and for people using the vanilla, this will be excelent, and if one say it once, one say it again, i praise your work

Then, to put in an idea for other people, as well as you. One could make it so that you have to do a side quest for a shop keeper, a friend of him or his family to be able to unlock the 50% off shop.

Then again, you can make turn it around, and instead of having quests, you can have reputation, which can either be Town, Guild or something simillar, just use your imaginations / game story, and make some space, and think of all the possibilities you can use this for!

Well, enough talking from me, keep up what your doing mate