Since the only first 75 yds of line on your reel spool sees 95% of the wear and tear, "topping off" with braid is the most cost effective way to go. I spool up from the arbor with hollow braided dacron (flyline backing) to within 1/4 inch of the spool rim, and top off with superbraid.

You can make a 100% splice by running 4-5 inches of the superline through the hollow braid, tie in a figure-eight knot in the 2-ply section adjacent to the cut end of the dacron. The hollow braid grabs hold of the superbraid like a Chinese fingercuff. Passes very nicely thru the guides. Backing lasts forever... only replace the superline every 3 or 4 seasons.