Pepto bismol works just the same in horses as it does humans. Give her 60ccs of pepto a couple times a day if possible.
Since you can't afford the scoping, the best way to actually determine ulcers is guess and check. If you can get your vet to prescribe Gidget a couple tubes of Gastrogard or Ulcergard. It's tubed paste like dewormer, but it's pretty pricy. (It cost me $75 for two tubes last year.) It's the very best for ulcer treatment and you'll notice an immediate change back into normal attitude.
However, since it requires a whole treatment plan, it gets really spendy really quickly. My vet knew that and that I'm in college, so she gave me an alternative method to a strictly Gastrogard treatment. If the Gastrogard or Ulcergard test more or less determines that she does in fact have ulcers, I would talk to your vet about figuring out a cheaper alternative. My vet gave me two large bottle of this wound cleaner called Draw. Abby was given 60ccs Draw/60ccs water twice a day in grain for a month. It worked because the main active ingredient was magnesium. However, I cannot for the life of me find it anywhere online.