My mom pays $425 a month for full board here in Merritt Island, Florida. It's the cheapest place around.
They feed twice a day, and give the horse hay whenever it's inside. They clean the stalls, take the horse in and out, wrinse it off if it's nasty and sweaty and grimey after being out in the heat all day. They'll also give the horse any suppliments or medications the horse needs, for no extra cost. If they're bringing the horse in or out, and notice it has a cut, or is limping or something, they'll call the owner and/or treat the wound. It's family run, and we're close friends with the barn owner and his daughter.
Board includes full use of the arena, wash racks, trails, tack room, and aisle cross ties.
The barn isn't the most beautiful, but it's shelter, and I can't complain... considering the management pretty much does everything for free. Considering how expensive everything down here is.