I guess I could hire a trainer for the other two mustangs, but I'm not sure yet what I want to do. What if they don't take to saddle? Does that happen often with 'stangs?
I don't know that it happens often in that particular breed, but there are some mustangs that are easier to handle than others. I lucked out with the 2 I got and didn't have any serious issues to deal with...no bucking, no rearing, no bolting, etc, just a bit of spookiness.
It depends on the individual horse and how it's handled. If the trainer handles a horse a little bit wrong, they can turn it into a bucker/rearer/bolter pretty quick...but that's with any horse, not just mustangs.
My biggest problem with this whole situation, I suppose, is that you are looking at completely untrained horses that are $1000+ just because they are mustangs. You could pick up a fully trained grade for much less than that (in my area at least, I've had multiple folks offering me broke horses for free that just needed a training tune-up).
Then, in addition to the outrageous purchase price, they are expecting you to either a) spend over $100 per ride to have them barely started under saddle or b) spend an additional $1000-$3000 with another trainer to get them trail-ready.
I know that it would have to be sight-unseen, but it would probably be cheaper to adopt one of the trained mustangs through the BLM adoption process (highest bid I've seen on any of those was $350) and then arrange to have it shipped to you.