Money-centric story beats
If the party spends at least 500 gp with the town blacksmith, he hires an assassin to take out the mayor. The more the party spends, the better the assassin he can hire, and the better the chance of success.
After the party buys an old, expensive book to help them complete a quest, the bookseller invests in an archaeological dig which frees an ancient evil.
Someone in the party has their pocket picked; when they find/chase down the thief, they find a family who is utterly destitute but makes zero apologies for stealing to survive (and will probably keep stealing if it gets them somewhere, though they’re not likely to say it out loud).
(High level) The party invests in a major business that ships valuable items overseas (good chance of weapons, with gems or even magic included). In exchange for a larger share, they have to accompany major shipments as high-end bodyguards.
Nearly everything has increased in price due to a new, unexplained sales tax. The people grumble, but businesses are hit hardest; now the businesses are hiring adventurers to find out why the government needs this money (hint: secret war).
A “discount” vendor who is selling stolen items with no way to trace them. The rarer the item the party buys, the more likely it is someone will recognize it and accuse them of the theft.
(Low level) The party is blamed for starting a bar brawl with a noble’s son and his entourage. (The blame comes whether they really started it or not.) Charged 500 gp in fines and damages, the party has seven days to find the money or be branded enemies of the crown.
The local government hires the party to investigate a rash of thievery. The party discovers a surprisingly large group of thieves at work, who say the lord is raking in every copper he can and the people are at risk of starving, so they’re giving the money back to the people. Turns out several of the people, who are never seen together, are different disguises of a single silver dragon trying to help the poor and take down the evil lord.
The party is offered a recurring job as city “exterminators”. What are they exterminating? Why is it there? Base it on party level and what kind of funds they should receive relative to their level and what they’ve already earned.
A local political bigwig has offered the party a place in his ward of the city. Either they can pay him for routine protection of whatever home or stronghold he’s offering possession of, or they can work for him when he needs help in lieu of payment.