Come to visit the Magic Store in Hyrule castle - we got any potion you need and much more things for a very low price!
We're in one of the best places inside the castle: Just go straight on to the market place and then turn right, it's the first house next to the church and very easy to find!
Inside the building you'll find myself as the vendor and a purple-dressed man who usually hangs around with us... Feel free to talk to him, he's quite a kind person.