10 gold skulltulas gets you the adult wallet (holds 200 rupees), 20 gets you the Stone of Agony (which supposedly rumbles when you're near a secret- never worked for me), 30 gets you the Giant's Wallet (holds 500 rupees), 50 gets you a Heart Piece, I believe, and all 100 gets you a purple rupee, worth 200 rupees. Those last two could be switched- I don't remember well.
SPOILERS
Dark-Link: What do you need a bigger wallet for to get the Biggoron sword?If I remember correctly you get the pocket cucco and hatch it, wake Talon, give it back, get the blue cucco, show it to the weird guy in the Lost Forest, get the mushroom, bring the mushroom to the potion lady in Kakariko Villiage, bring the medicince to the Lost Forest, show it to the Kokiri, get the saw, show it to the carpenter in Gerudo Valley, get the broken Biggoron sword, show it to Biggoron, get the prescription for his eye drops, bring the prescription to King Zora, get the eye ball frog, bring the eye ball frog to the old guy at Lake Hylia, get the eye drops, bring them to Biggoron, get the claim check, wait 3 days, and get the Biggoron sword! Are you trying to get Medigoron's sword and breaking it?