It's "Song for Bob" from The Assassination of Jesse James by the Coward Robert Ford soundtrack by Nick Cave and Warren Ellis.
While for the $75 price range I will stick with a manufactured slider, but I will say that in a pinch, this would be a great substitute. And if you wanted to, you could get the rails at practically any length and build a long stinkin' slider. And you could take their idea further and with a little ingenuity, you could turn it into one that could go vertical as well. A lot of possibilities here.