If they make sense for the area, sure. If they do not, I'd raise the price, but allow it given time for someone to procure one. The difficulty in doing that would depend upon the distance from their natural grounds, etc... In many of my campaign worlds, I historically have orcs, ogres and (the smaller) giants use them as siege weapons/mounts (once trained, I give them the siege property (double damage on objects) and allow them to carry up to 1600 lbs - enough for up to a hill giant to ride). I have a gargantuan elephant/mastodon with a Tolkien name that I allow as mounts for larger giants.
Those suggested upkeep costs are insane unless the PCs live in a desert or otherwise provide all food for the elephant. Remember: Elephants don't have anyone caring for them in the wild and they survive (0 upkeep). If you have enough land, they care for themselves.
They're not carnivores like Hippogriffs or Griffons (by the way - griffon feed is 2 silver per day), so they are cheaper to feed - although if you package it to feed them rather than letting them graze, it is a lot of food (more than 70,000 calories, several hundred pounds daily taking at least twelve hours to eat - maybe up to eighteen hours). If you bought that much food to provide to them, it would cost a lot, but if they have a sufficient grazing area (a big area), the cost would be minimal. They also require 20 to 50 gallons of water daily. Also, if they have to bring food with them when traveling, they can carry food and water for about one day according to their capacity - if they do not carry a PC. However, if you were to buy that much hay, vegetation, etc... it would cost one laborer one day to collect for each day - a skilled laborer would be 2 GP per day, but I'd argue you do not need a skilled one, so 2 SP per day would suffice. You might have to pay a fee to get access to the vegetation, buy horses and a cart, etc... but the cost should be closer to an initial outlay of maybe 100 gold and then 100 more gold per year, plus medical costs, etc... Now, if you have to ship in that much food, the 2000 annual costs seem more appropriate.
If used as a mount, they'll eat as they walk and drink when they can (which must be often), but that much exercise requires more food and water for the elephant.
I'd suggest to DMs that they have an elephant require multiple goodberries to survive (my rule is 1 berry per square occupied - so 9 for a huge elephant), but it is a good solution for the food, but not the water, needs.