Is buying a tape, the price of which is 330 shekels, every 5 or 6 months, or annually, after saving up its price, considered extravagance?

The ruling is based on the value of the cassette, its benefit, and your need for it. Extravagance is spending money inappropriately, and there is no extravagance in doing good deeds. Therefore, if the cassette has a permissible value and you are in need of it, then buying it would not be considered extravagance.