Check around for a good used 1980s-'90s "mountain bike" -- those older rigid fork bikes were closer to what's now lumped into the hybrid genre.

My '92 Univega Via Carisma came with a Shimano Exage 500 CX group that's virtually identical to the Deore group of that same era. I have both the Exage 500 CX and Deore LX long cage RDs. One is labeled RD-M500, the other RD-M550. There are negligible cosmetic differences. Same with the Exage/Deore front derailleurs.

Depending on your local market you might luck into a really nice group on a chromoly frame/fork bike for $200 or less.

BTW, I have the same preference for casual group or solo rides. If I'm on my road bikes I'll turn every ride into a workout. But if I'm on my Univega I'm more relaxed, sit upright and enjoy the view without turning it into another attempt at Strava PRs. I even switched from flat to albatross bars to make it even more pleasant to ride casually.