So a few months back I did a bunch of logistics calculations on maintaining a bunch of soldier hirelings, the supplies needed to feed them, shelter them, transport goods, feed the horses, provide water and so on in DnD 5e.
I am now wondering about the same basic math, but replacing some hirelings with elephants and going full elephant cavalry, and also the variant using horses and going for conventional cavalry.
Elephants eat a lot, it works out to about 600 pounds, or 3gp a day in feed or a long time spent foraging if you aren't using goodberries to feed them. They also need a lot of water, about one and a quarter 40 gallon barrels a day. Obviously this makes for a lot of food and water that needs transported if you can't rely on natural sources, and you can never really rely on natural sources.
A dnd elephant can pull 6600 pounds, which means one elephant drawn wagon can carry supplies for the animal for just over a week. This is much worse than the maths I had done in the past for horses, oxen and donkeys, but elephants in dnd are much weaker than real ones for various stupid reasons.
So elephant cavalry is impractical without a bunch of horse drawn carts carrying food for the elephants, plus people and gear on top of that. So they can be written off as a dead end for hireling mounts. If you need two draft horses and a wagon just to carry feed for one elephant for a week things are going to get impractical fast.
Horses are much more economical to feed, and can carry huge amounts of cargo in excess of what they need to eat and drink even with their pulling capacity being much lower than real life horses. If you can get past the hurdle of saddle and warhorse costs then a couple of draft horses, or oxen if you really want to pull a lot of supplies, can be the baggage train for a dozen cavalrymen. Warhorses cost twice what an elephant does by the way, which seems quite insane.
EDIT: If you can persuade them that a diet of chickens, goats and the odd bandit is a good deal* then worgs are also surprisingly economical mounts, and they're as smart as orcs to boot. Obviously there's no real world equivalent to base their dietary needs on, but grizzly bears seem like a good rough starting point, and it works out to about a goat a day depending on the size of the goat. Goats are only 1gp, which is half the price of a normal skilled hireling.
*It's a great deal compared to what the average goblin can give them.