I'd be happy to help you out with this, I just have a few questions. Is this a one-time task for you or will you have to do this repeatedly with fresh data? If this is a one-time deal, it sounds like simply getting the data to match line after line and then inserting a pivot table which will give you the summations you're looking for. If you will be doing this again and again with the same combined reports, a macro would help to quickly order the data for you. I can help with that also. What version of Excel are you using?
My day job is accounting and I work with a lot of reports that come over to Excel from outdated software and I have to tweak the documents before I can really work with them. I'm certain that I can help you get the information you need out of the reports you're working with. I look forward to hearing from you and good luck with your project!