Thinking of something strictly for a modern/urban fantasy setting.
So one of the things I really liked about d20 Modern (way back in the day), it had an abstract d20 system for making purchases, representing the ability for characters to use credit and other means to buy items while shopping. As you purchased items, you lost your bonus to your d20 roll and it was more and more difficult to buy items. Additionally, items with a DC equal to your bonus you could easily buy with no change.
I'd love to have a feature like this for my modern/urban fantasy setting. I don't want to keep track of money, credit cards, bills, etc. It could also represent purchasing or gaining funds from legal/illegal means (i.e. credit card fraud, like in Supernatural). Has anyone come up with a cool system using the narrative dice to represent buying items, besides the Negotiation and Rarity levels? I'm sure this narrative dice system could support something very interesting.