No other NGK plugs that are cheaper than the originals will last as long. Why not just purchase 4 of the correct plugs now and do one side of the engine, and purchase the other 4 next month and do the other side? All 8 plugs can be purchased for less than $100 at
www.sparkplugs.com considering the amount of labor it takes to change them , it is not worth saving a few dollars for a cheaper less long lasting plug.Do you really even need to change them immediately? If not, buy them a few at a time if need be and change when you have paid for all 8