I just checked, there is no way to transfer, sell, or even delete accounts (without contacting Mojang directly, that is). Minecraft is not sold in physical copies. Anyone can download the client for free. The account is simply used to download the game data files the first time as well as play online.

As Rei said you should've just bought it when it was cheap, but 20€ isn't much anyway. I'm surprised you don't have it already, it seemed to me like most people on this forum had at least tried it once.