I tend to view modern RBs like I view relief pitchers in baseball. Most teams can churn RPs internally without much of an issue, and they tend to be reasonably interchangeable with minimal resources needed to acquire them. Take Andrew Kittredge; all the Cubs needed to trade for him was a lottery ticket. It's also generally a fool's errand to spend a high draft pick on a guy who's a relief pitcher in college.
However, all of that goes flying out the window when you find a really, really good RP. In that instance, it can be worth the hefty price, be it draft pick, trade pieces, or contract.