I may have to steal your 3 page binder idea for receipts and records! You just use the plastic page inserts?
I have a big 3 ring binder, then divided it up into Service and Modifications with labelled tabs to separate the two sections. Everything is in chronological order from oldest date to newest date. I was able to track down all the old service records from the dealer that serviced the truck before I bought it as well.
I put all invoices, receipts and records in the heavy duty page protectors so two records could be easily viewed. As mentioned, I'm working on an expense spreadsheet just to see for myself (not including miscellaneous consumables, like spray paint, waxes and cleaners etc....) I do have all the invoices for paint ordered from automotivetouchup.com just because it was a couple hundred dollars over time.
Bit OCD, but I do the same thing at work for records, accounting and reporting as well.