I wish there was something that automatically aggregated them though. I have hundreds of emails from iTunes Store from 3 years back until today. I would be interested to see how much I have spent, but I'm not sure I'm willing to go 1 by 1 and paste them into excel..
That sounds like something that could be tracked/accumulated by your personal App Store account. It should be easy for them store that info with your store ID or iCloud ID accessible under an account management menu item, for example.