For starting our journey together, I had to give what was most precious to me. Another was my magic staff in exchange for a way to reach a castle in order to retrieve one of Sakura-chan's feathers. The price paid for making sure everyone arrived to a safe world after Celes was paid in part along with someone else ... my part was to use my own magic. And the fourth ... I suppose it wasn't necessarily my price.
I believe there's more, but I don't remember them yet.