Walbro Ignition modules range from about $24 to $47...
They are just bolt on coils, so if the coil on your engine was originally bolted onto the housing instead of the cylinder they can't be used...These small engines run the same no matter how you control the spark, whether fixed at 28 or variable. There is nothing that can be done with the spark that makes any difference at all in performance, other than retarding the spark for easier starting...If the spark jumps the gap under compression the engine works..A 50,000 volt spark won't make the engine RUN any better that a 20,000 bolt spark..It might clear a flooded engine faster, but once running the engine doesn't care....