If your DM is alright with porting over 3e items, Stronghold Builder's Guidebook has Bed of Wellness (Remove Disease). It has a market price of 15,000 gp, and it casts Remove Disease on anyone who lies in it for 3 consecutive rounds. There's no upper limit on how many times it can function per day, except that there are 14,400 rounds in a day. So one bed can cure 4,800 people per day, if you use it around the clock and somehow get the time taken to get people in and out of it down to zero.

Or you could bring out the big guns. The same book also has Platform of Healing, but in the interests of full disclosure, inform your DM that it was later reprinted in Draconomicon with a higher price tag. It has a market price of 76,500 gp for the Draconomicon version. But regardless of version, it casts heal on anyone who gets onto it. No 3-round delay here, and it loses the 1-person-at-a-time limit too. It's 10 feet across, plenty big enough for multiple people to simultaneously be clambering onto and off of different sections of it simultaneously.

If you opt for the second one, you won't just solve all disease in the city (and surrounding area) forever. You'll also solve nearly every source of mundane harm. Missing limbs and death are about the only things Heal can't deal with that aren't necessarily magical in nature. … Oh wait. I guess there's still starvation. Better build an Everful Larder too.