Is one $0.5 for 1 month or for what time? 'coz spotify has monthly payment for premium account.
And BTW Spotify is giving out free trials. Are you trying to sell trial accounts?
EDIT: It seems to be that Spotify is not giving out free trials in the USA, only in my country. They only have a $0.99 three month offer.
These are 3 month Premium accounts that you get to choose the user/pass to