Rope
I get most of my rope from Home Depot, or Wal-Mart. They carry 3/8", 5/16", and 1/4" line for a good price. It is not as strong, but our small boats don't really need that much strength. We could be using 3/16" line from the marine dealers and still have more strength than we need, but it would be so small as to not be comfortable on your hands. There are lines at the Marine store that can give you 9,600 lbs of tensil strength on a 1/4" line and you can even get 800 Lbs of tensil strength out of top of the line 1/16" line. So you will have plenty of strenght and the larger diameter line with the cheaper rope. Now for my 30' boat I buy my sheets (5/16") at West Marine (3,300 Lbs tensile). But there is a lot more force on that 150% genny than any line on a Mac will ever see. I have used 1/4" from Wal-Mart for 4 years for my Mac halyards, and 5/16" for my sheets (not because I needed the strength, but for comfort) and have never parted a line on the boat. I did break a 5/16" line dry pulling a Mac back on the trailer in my yard, after working on the swing keel. And I think I would rather break a cheap rope than have a sail blow apart. Anyways, you can't even pull hard enough to break a cheap 1/4" line with out a winch, even with a 4:1 pulley arrangement. Wal-Mart 1/4" line has a tensile strength of around 1,700 Lbs and a SWL of 700-900 Lbs. I wouldn't winch some-one up the mast with it, but it's good enough for sails. Do grab the book at the Marine store and learn how to splice it. A splice is much stronger than a knot. Knots can weaken a line by up to 50%.For dock lines use the laid (3 strand)nylon rope. While you don't want the streatch this line has on a halyard or sheet, you want dock lines to have some give. Same with anchor lines. The give helps reduce the shock on your cleats, as the lines load and unload. Learn to splice this line too.