Amazon offers Prime members the Mr. Heater Buddy Series 10-Foot Hose, model no. F273704, for $13.36 with free shipping. (Non-members can spend $49 to qualify for free shipping; otherwise, it adds $7.54.) That's the lowest total price we could find by $4. It's compatible with the Mr. Heater MH9B Portable Buddy and MH18B Big Buddy.

Note that this item is expected to ship in one to two months.