This procedure is quite common, and the majority of mares or fillies have this done. Actually, it is recommended to have it done before problems occur. When they suck air they also suck in dirt which can cause infections, so most of the time this procedure is a preventative. Just think how low they get when they turn a barrel?
Around in our area it runs about $75 to $80 bucks, and boy let me tell you, it's painful to watch and makes you hurt, but they don't feel a thing since they numb the area. Just like tying your shoelaces, or that's what it looks like, ouch!!!
Funny story, I have a horse off the track that only was in one race and I planned on having her sewn up so I took her to the vet and to my surprise, she already was done! Quite a nice surprise, I never thought to look myself! EMBARASSED