I have always bought most of my horses and a mule from auctions. I realize you aren't as knowledgeable as some so I would give this advice. There are generally two types of horse auctions, regular and select. At a general auction there can be very good horses that sell for cheap ($1200-down) , but it takes experience and a little luck to find these types . Also, at these auctions are the rank, unbroken, lame, problem horses that people are trying to dump. So, if you go to an auction make sure you bring someone that has experience and can tell the difference. Up in Montana there is a auction in Billings called BLS. It is a good auction that has the type of animals you are describing that sells in march called the outfitters sale. I would not consider this a select sale but close.
The second type of auction is the select type. These auctions are held every year and typically have the same sellers. They catalog the animals and give a brief description and picture. Sometimes the sellers will preview the horse by ridding, roping or packing to show off its skills. These types of sales are safer and sometimes are guaranteed or your money back. I bought a mule at a select sale this spring and could not be happier. Of course the down side is your going to spend some extra money at select sales. There is a good select auction in Salmon Idaho in May, both horses and mules.
I have bought many over the years at sales, and thank god have never picked a bad one. The few I did own that didn't work out i bought from friends, go figure. Take your time and go to some auctions and just watch. You can start to figure out which ones are the calm quite ones that you should buy. You don't need the horse that the seller is running and spinning in the sale ring. Look for the ones that are quite and have a good handle. I looked for three years before buying my first mule. I bought him at a catalog select sale. He wasn't finished like some of the others but he sold for cheaper and I will just finish him myself. Good luck