"Good" and "cheap" rarely go together, unless there is problems with the horse (mentally or physically). You usually have to pick two and compensate with the other.
Anything good and cheap, won't be sound. Anything cheap and sound, won't be good. Anything good and sound, won't be cheap.
As for an answer to your question, it depends on which country you are in. Facebook is still a good way of sussing out horses though, even with the ban.