I'd start backward, Sparkplug, ignition coil, CDI box, and then the pickup on the stator. All should be really cheap unless you want OEM. If you got the manual should be something in there about ohming out the coil to see if it's bad. Should be able to do the same for the pickup if you can trace the wires out on a schematic.
Either way cheap aftermarket parts you can do the CDI and coil for maybe $50. The stator is a bit of a pain to change but it's not bad takes a hour or two and you get the change the oil with it.