Check these out:
The 99 Most Essential Mozart Masterpieces - Only $0.99 for whole album! This is a daily deal according to Amazon's Facebook page, so buy it fast.
The Classical Halloween Collection - $3.99 w/$2 credit
NOW That's What I Call Music Vol. 39 - $3.00 w/$2 credit
Also, check out the 100 for $5 section! There are some great albums in there that will only cost you $3 with your credit.