Wait for their end of the year sale, or the Black Friday discount codes. Last year they did an interesting promo where you could unlock better and better discounts by using previous ones, but you didn't know how big the discount was unless you used the previous one. It ended up working like this:
September: 15% off coupon via email, sent to all subscribers.
October: 25% off coupon via email (ONLY if you bought at least 1 song using the 15% off code).
November: Black Friday, 40%(?) off.
December: 50% off coupon via email (ONLY if you used the 15% off code AND the 25% off code).
This was a smart strategy: they slipped the Black Friday discount in the middle to try and entice people to buy their carts before the massive sale. I didn't fall for it - I bought 1 song using the 15% off, 1 using the 25% off, ignored the 40% off, and bought my entire cart at 50% off.
Just wait for December to roll around; I'm sure they'll do something similar.