I bet those MD-80’s that everybody just retired are available and probably relatively cheap, in a pinch you could pull out all but the first class seats but keep the lavs and galley(s) and you’d have plenty of classroom and coffee break space to accommodate 2-4 students I would think. And you have experience operating the type for profit, so you’d be set!
ETA: Honestly, Citabria looks like it checks all the boxes. A little pricier than a 140 or champ, but those have gone up too (I just looked and it looks like you could add $10-$15k to the market prices five years ago). I’d be inclined to look for one with the Lycoming motor though, IMHO.
I really like the idea of the Grumman’s, they’re neat aircraft and you see a lot of them in these parts. The only problem I see with them as a primary trainer is the castoring nosewheels (steering with brakes). I’ve flown with a number of brand new FO’s in their first jet who had learned to fly in various LS or Cirruses, and with a few exceptions they had a habit of riding the brakes or using them for steering. That (anecdotal) experience makes me a little leery of those types for primary trainers. YMMV. They’re definitely sweet aircraft.