An answer from a novice here...
A prop is more efficient than a jet, generally speaking, it is moving a large mass of air at slow(er) speeds, compared to a jet propelling the air very fast which creates a lot of losses in efficiency. On a per hour cost, you will probably find a 50 seat DCH8 is significantly cheaper than a CRJ.
Anyone with knowledge care to post a 1 hour block fuel burn for each of these aircraft as a starting point?
However, over a sector of about 3-400nm and above, the speed advantage of a jet will make up for those losses and allow for greater utilisation. On short sectors the difference between a jet and a turbo-prop will only be a few minutes.