Unless you fly alone - I do NOT recommend fishing line. Same material, different weave. Look on the major online kite stores for bulk spools, sleeving, and don't forget winders. Look on A Wind of Change for components. I find you can usually get 2 sets for the price of 1, but you also invest the time it takes to make them. All comes down to what your time is worth...
I buy commercial sets, then equalize. Saves me the time of setting up and getting it all arranged. One adjustment and usually I'm good to go for a awhile. One more adjustment and usually pretty safe, unless flown in extreme conditions.
I usually go thru 2 sets of quad lines every year. I fly team mostly, lots of crossed lines there. I almost always go thru a set just at WSKIF every year. Team flying almost every day for a week solid eats that set fast! Old lines get thrown in the practice bag, maybe cut down, etc.
About lines - if you fly on a beach - wash them out - lots! Take the handles off and dunk the whole set, winder and all, in a container. You will be surprised at how much sand comes out. Plus the dunking dissolves the salt crystals that build up on your lines. Ever look at sand or salt under a microscope? Sharp!! Eats lines fast! Clean them!!!