I've known of success with treating ulcers with papaya
Because it contain papain which I've also fed to my boyfriend for heart burn... papain is a naturally occuring enzyme which resembles pepsin which stimulates the appetite, soothes membranes of the esophagus and stomach, and quiets inflammatory bowel disorders. Papaya also contain Vitamin A, Vitamin C, calcium, iron, niacin, potassium, riboflavin, and thiamin
As stated above the reason this generally works is because of the ratio of magnesium and calcium long with the very important papain
Unlike other medicinal treatments which aren't always safe for longterm use or ... practical $$$... papaya is affordable and can be used everyday
Two ounces shredded in with his feed should help with the ulcers and sooth his tummy
Read more: What to feed and how to feed it! Flax Seed, Beat Pulp, Rice Bran
Also papaya can be used as a prep for anti inflamatories because it coats the stoumach and makes it more able to absorb the medicine.
Also for the eventers out there it prevents caustic burn that sometimes is associated with feeding electrolytes to horses which damages the esophagus and stoumach. Especially prevelent when feeding frequent doses of electrolytes.
Helps old horses with digestion, young horses with scours, mild blood thinner... the list goes on and on...
End of story is its cheaper than 900$ and maybe worth a try or talking over with your vet