I don't know about conversion barrels for the Sigs, but if you want a good accurate and fair priced 9mm conversion barrel for your G23, I would look at Lone Wolf Dist.'s own brand of barrels. You can get one of their stock length, ported or threaded 9mm conversion G23 barrels for $99.95. Their own brand of barrels are match grade, but have been pre-fitted, so they drop-in with no gunsmithing required. Here is the link on their web page:
http://www.lonewolfdist.com/products...&curRecIdx=161