Hi Jessie,
We just had a mini barn containing 4 stables +feed/tack room + wide central corridor built. The cost was about £11.5k (incl VAT delivery and erection) but we had quite a lot of extra upgrades (extra thick kickboards, sliding door at front, portal frame construction, external top half doors, sarking board lining under the roof) which added more so it ended up as £15k ish (incl VAT delivery and erection).
I know that sounds crazy money but it is a barn so you can store hay etc if you dont use all the stables.
Whatever you build for however much, bear in mind the extra hidden cost of the base, drainage, water and electric. Esp if your site isnt level. All this probably added £6-8k onto the costs of ours - on top of the stables costs, I couldnt believe how much a load of concrete cost, and how many we needed....:-(
I do know lots of peeps who use a field shelter and then stick stable doors on the front though, would be a lot cheaper but we are v exposed location so need luxury accom for the pampered ones.
We used Saltire to build ours (we are in NE Scotland), and they were pretty good. Would use them again.