My question… should maybe have been asked as “what does a lower level dressage horse move like”
If I were shopping for an inexpensive horse to do lower level dressage (Disclaimer: I know nothing about Western Dressage), first priority would be three correct gaits, as has been said above. Next would be suitable confo: level topline if not uphill, certainly no downhill build, not post legged behind, not long backed, neck put on correctly - have the conformational ability to stretch down and come onto the bit. Next would be some overtrack at the walk and trot, next some natural rhythm at the canter, next some natural suspension in the trot. I would insist on a good walk, as that’s the gait that’s hardest to improve.
I think you can find all that relatively inexpensively. There are lots of really nice Training/First Level horses that struggle with Second Level work and are not going to go farther than that.
I tend to be leery of stock breed horses for dressage prospects, as they tend to be downhill and not have much reach/stride. Or if they did have it, have had trained out of them.) I’d be especially leery of a stock breed that’s been trained in another Western discipline, as that training tends to make them very reluctant to accept contact or reach for the bit.