I've built both. The fly swatter version works fine, the ion generator version works better. If you can build the ion generator version for under $40, then I would recommend doing that. If it cost more, you can make the fly swatter version for under $10.
And it's been a while, but IIRC, the ion generator version doesn't have the discharge zap of the fly swatter. I wouldn't call this a big deal, but it definitely comes into play when using it.
Jason