The Miller 211 is a good option. I got one on Craigslist for $1200 like new, though I hate the little M-10 gun, they can take a M-25 like I use on my Miller 251.
Flux core sucks, I’d avoid.
Hobart are good machines, Miller owns them.
I’d have better recommendations if I knew your sons application for the spray gun.
There isn't anything really wrong with flux core. You just have to clean up the slag from the welds when finished. That is the biggest difference from what I've noticed. The beads aren't quite the same as I can get from MIG, but it is darn close. Penetration in the same.