To get money in Ocarina of Time, whenever you want, wait until the beggar living at Hyrule Castle Market moves to Kakariko Village (once you are an adult). Go behind the Potion Shop and into the grotto in the village, where you will find a fish.
You can fill an empty bottle with a fish each time you enter the grotto. Each fish sells for 100 rupees to the beggar, so if you have enough bottles, and the patience to keep going in and out, you can generate an unlimited amount of money.
Added by: MongooseGeneral Jun 23rd 2011, ID#63