Because others have suggested MA but voiced concerns about the weather, let me suggest the South Shore! I moved to the South Shore recently from the 495 area west of Boston and have been very pleasantly surprised by how much more mild the weather is here (I am only about 3 miles from the ocean). So far this winter I’ve used my medium weight blankets three times – otherwise temps have been mid-30s to mid-40s (tomorrow we are in the low fifties!) and 100 gram blankets have been entirely sufficient. Lots of days they have been completely naked. I have only worn actual winter gloves on the days when it dipped below freezing.
In the summer, I see the very occasional B52 fly (my neighbor has animals and does nothing about fly control), but generally my horses are very happy with just some fly spray and fly masks.
Yes, property prices can be a bit nuts, but it is very localized. Some towns are pricey, but other towns right next door have surprisingly reasonable prices. I see lots of equestrian property listings in the Rehobeth area that are very reasonable, for example.
I’m still getting to know the equestrian community around here, but I get the sense that there are a good number of trainers. The vet situation is a little concerning to me, but again I think it depends on where you are. Just a little bit further south of me and it seems like there are lots of good vet options. (I have a wonderful vet but I worry about my options when she retires.)
Feel free to PM me if you want to chat more!