Good income/expense tracking tool for side projects?

I have a side project and would like to track my income and expenses so that when tax time comes it's easy to supply the necessary info. I'd like to be able to attach receipts. I don't need to do payroll or have team members have recurring payments or anything like that.

I'm using Google Sheets right now and storing receipts on dropbox, but it'd be great if there was something simple and cheap to store it all for me. Quick books seems too complicated for what I need.