Producers of Backing Tracks usually retrieve their investment in creating the recording and finding and paying musicians and producers by selling the same track over and over. That's why it only costs a couple of pounds/dollars to download a track.
But if you require a track for your own exclusive use, it can cost considerably more. but perhaps a lot less than finding and recording your own musicians for a project.
And you will know you have a track that's completely original with no copyright issues.