Southeast RC engines, and Valley View RC have the RCEXL ignitions down to around 50 bucks or so. I would go with that instead of a magneto myself. A good bit less weight, easier starting, and a bit more power...

The "repower" new long blocks we are talking about from online small engine parts suppliers come without carb, muffler, and magneto/ignition for around 220 bucks. It is hard to find a good used backpack blower without having to pay a bundle for it.

AV8TOR