Won't $15 buy you a new one ?
Not one worth having. You don't want to be buying fire extinguishers, like those cheap Kidde or First Alert extinguishers, at Walmart or wherever. They're fine for the house, but out here, not so much.
Also, if you go to the stores that sell those extinguishers, check out the kinds of extinguishers they have on the walls and pillars around the store, see what they would use in case of a fire.
If you ever need one for an engine or electrical fire, you don't even want a standard dry chemical extinguisher, you want a Halon or some other clean agent extinguisher (Halon 1211, Halotron I, etc). Granted, a dry chemical fire extinguisher used on an engine, fuse block, wiring, or electronic equipment is certainly preferable to not using anything at all, but the dry chemical will corrode seals, wiring and connectors really badly, and the cleanup can be amazingly tedious and labor intensive. A Halon extinguisher leaves zero residue. You just don't want to use a Halon extinguisher in an enclosed space. A Halon extinguisher will cost you some money, but if you ever have to use one on an engine, it's worth every penny, times 10.
A little 2.5 pound Halon extinguisher by Amerex will cost you about $150. The same 2.5 pound dry chemical Amerex costs about $30. A 5 lb Halon $225, 5 lb Halotron $133, 5 lb dry chemical about $35.
For example...