Leader Fishing

Yes, monofilament leader is the same stuff as monofilament line, and yes it is sold in shorter lengths (10-50 yards or so, I think.) They also sell fluorocarbon leader, which is more expensive, but much more nearly invisible underwater.

And yes, it is sold at a higher price per yard in the shorter lengths. It's sold that way mainly for people who use heavier mono or braided line as their main line and may never need a full spool of line of that strength. If you have a bulk spool of the size of line you want to use as a leader, go ahead and use it. But don't buy a bulk spool expecting to use it for the rest of your life, because monofilament does degrade after a few years.