Music is a tough sell online, especially in the PPC realm.  You’re taking an item that doesn’t have any distinguishable difference between your version and a competitor’s version, and trying to give the customer reason to buy yours.  Like grain, gold, and oil before it, music is now a commodity, and selling commodities online is a totally different game than selling another type of product.  So how do you do it?  You have two main options:

Play the numbers: If you can’t add value to the product, you have to know your limits on what you can afford to pay for the sale and stay profitable.  Let’s say you sell a CD for $10 retail, and you make $4 in profit.  You only want to use a portion of your profits for marketing, say $2, so this becomes your maximum acceptable cost per sale.  If you know you can convince 1 out of 10 visitors to buy from you instead of the other guy, then you can afford to pay $0.20 per click.  This is your maximum allowed cost per click.  However, you can go lower.

Using all your PPC skills and knowledge, you can bid lower and still get the quality levels of traffic by having really creative ad copy that grabs attention, or ignore the expensive engines like Google and only use Yahoo.  Have you considered shopping feeds?   There are lots of options here, and some might be cheap compared to what you might be paying

Add value: Instead of buying a transaction, what if you create a recurring customer?  Get them to the site with the CD, but give them reasons to stay.  This may be through background information on the making of the album, embedded videos of the best songs, interviews with the members, or tweets from their most recent concert via Twitter, etc.  If you’re able to offer the visitor an experience instead of just a product, then you have the opportunity to make future sales and pay a lot more than only $0.20 per visit.