A couple years ago, before the Covid gun buying frenzy, you could find a Sig 2022 for $400 easily. Don’t know what they go for these days. I know they’ve had a bit of a resurgence in popularity.
A quick check shows a $597 MSRP. Mostly I see it’s around $500 (if you can find it in stock) Add FFL. shipping, extra mags, and $600 would be more than fair. Pretty decent Christmas present for a 15 year old. Sounds like a pretty wacky family, from the little that I’ve seen. Nothing wrong with having a premium wonder-9 in the safe. Can’t see letting a kid run around with it.