If you want to buy on PSN without a credit card, buy a $50(or whatever denomination) PSN card at your local game store. You enter the code on the card and your account is accredited the amount that you bought. No credit card needed.
Even if the open windows of science at first make us shiver after the cozy indoor warmth of traditional humanizing myths, in the end the fresh air brings vigor, and the great spaces have a splendor of their own - Bertrand Russell