In Kakariko Village, in The House of Skulltula, first kill 30 Skulltulas to get the Giant Wallet. Then kill 100 Skulltulas to get a Giant Rupee(which is worth 200 Rupees). Get the Giant Rupee then exit The House of Skulltula, re-enter, and you can get it again. Do this over and over when you're low on rupees so you can buy whatever you want, whenever you want. Enjoy!