Is there a way to differentiate between paid and free apps in iTunes purchase history?
In addition to keeping your email receipts, you can also view your entire purchase history by viewing your account in iTunes. If you're signed in, click your account name in the top right, and choose the "View Account" option. On the following screen, the third section down shows "Purchase History", with a link on the right to see all your orders. You can see each order, listed chronologically, and jump to specific months and get more detail about a specific order.