The O'Donnell's sport plugs are very durable and cheap.
www.towerhobbies.com has them. Usually for 25 bucks roughly for 6.
If you are going thru plugs that fast you are probably running way too lean on the HSN. Richen it up and lean the LSN to get the performance back.
What car, engine, plugs and fuel are you using. How much runtime is on the engine?