I have seen barns older established trainers have built in the past few years.
Those trainers had previous barns built with lots of interaction between horses.
Interesting, newer barns have more privacy between horses, are not as open.
They also are made so horses can’t “reach and touch” another, the source of bites, some times serious injuries from it.
Talking to them, they said that they too thought the more open, the happier horses.
Well over years, they learned that horses will tend to fuss more when they have neighbors right there and can reach them in any way even thru narrow set bars.
I was thinking, makes sense, barrier aggression as fun and games and can make for grumpy horses that end up just pinning their ears at the world from that kind of life.
Some horses like others, some don’t, some like others at times and at times not, or not in their space, looking at them all day long.
Now some have stalls with “windows” in that division wall, solid front and back, opening in the middle and that opening mesh horses can “talk” thru with a neighbor, but can’t take a bite out of them, if in play or seriously.
They told me that has cut down considerably on those injuries and those of horses kicking at each other because of being annoyed.
Now, the front mesh doors are good for air flow, although some horses will paw at doors, like at meal time, so be sure to have something that if they bang the door won’t hurt themselves on.
I don’t think there is a perfect barn or stall model.
There are trade-offs and it would be nice to have several options.
A few smaller and bigger stalls, some stalls solid between stalls, others with openings, or a way to open or close the space between them, etc.
Building a barn we learn all along and once using it, we realize we could do better, is how we learn.
As for price, it depends on what all you want to make your stalls from.
One good way to check prices is commercial portable stall companies, like Priefert or any one that sells the kind of stalls someone wants to build.