If you’re willing to give away your financial information (not your actual access codes, but the data of what you’re buying), then you can use a web service like Mint or Wesabe. In exchange for their services, they collect your data (anonymized, but likely with each transaction associated with each other) and use it as they will, often for their personal profit.
A locally installed application such as Microsoft Money or even an Excel spreadsheet has the benefit of keeping your data secure and private, but it’s more work for you to enter items.
Honestly though, tech is often more hassle than its worth especially the spreadsheet method if you do a lot of debit/credit transactions. Based on your question wording I get the impression that the physical book works fine, other than your son drawing on it. So the best solution to your inquiry would be to stop having your child draw in your book. I think this is a great opportunity to teach him boundaries and ownership.