Tbh miniature donkeys would probably not be a good choice...they may be feisty and sturdy, but against anything more than a small coyote, I doubt that they would be of much use. It's the reason alpacas can't be guard animals. They are just too small. I would go for a regular donkey or llama. However those can sometimes be as expensive as a dog if you want a reliable one. As for the care and such, they are animals

You won't be able to just throw them out and hope they don't die. They need at least the same care as goats(I'm almost certain donkeys require hoof care, not sure about llamas), they probably need more food than goats, and any other regular care like vaccinations, wormings and such. However llamas and donkeys are only good against one dog, coyote, or something like that. They won't be able to handle packs or bigger animals. And you can't get more than one because they'll bond together instead of with the goats, which means they won't guard. And like wildegoats23 said, they can get aggressive(and when a 400+ lb animal gets mean, it isn't good) and you can never let your family dogs near them as they will probably get trampled! As for easy keeping and general temperament, it depends on the animal, just do your research on all your options and decide from there.
To be honest, I would save up for a good LGD. They are completely worth it, reliable, small(smaller than the other options), and efficient. They also probably will cost less in food. You may have to get two of them if you have a big predator problem, but it's still better in the long run to spend the money and protect your animals than spend a little less money and have most of your animals killed. Sorry to be blunt, but I'm just thinking practically
