I had a dairy, beef cows and horses. I had draft horses because I liked them, not because they were cheaper than tractors. A tractor is much cheaper than any draft animal over the course of their working years. Many classic tractors are way overpriced because many others want them, too. For example a Ford 8N is worth double of what it was worth 30 years ago. Your best bet for low cost is a new made in India tractor.
A draft animal needs some other feed than what the small farmer can grow, like balanced grains, and vitamins, worming, vaccinations, shoes or you end up with a sick or dead animal. Then there's the harness, horse collar, single tree, reins, all needing constant attention or they fall apart. A horse needs about 3 acres of good pasture. Otherwise in the rainy season, all you have is mud. A working horse needs 25 pounds/day or more of a good grain mix. Maintaining good pasture with feed value means plowing it under every 4 years or so and reseeding.
Farmers, before tractors, had about half of their farm dedicated to animal food production. Failure to properly feed a working animal causes eventual death.