I've done somewhat similar work. I found it best ultimately to pull individual transactions -- as a text/report dump -- and then work them up in a combination of Excel with hooked in regular expression support and Perl and whatever else (i.e. for a front end interface). Excel provided a convenient interface for necessary manual sanitation. Perl provided enough speed along with flexibility and further pattern matching. Other stuff made the results accessible to accounting staff.
For my purposes, SAP was a giant data entry system. And a crappy one, at that, as one of the most important fields for my work was not a field, but one of an arbitrary number of entries glommed together in a free text field where only the maintenance -- or not -- of data entry conventions by the many individuals creating records provided any degree of sanity.
Thank goodness for regular expressions!
Separately, it's not just the "sexiness" of the problem at hand. It's that in typical SAP environments, the level of bureaucracy to get anything done is overwhelming. Your technical problems are far and away secondary; for example, just getting what you need on a report, any report, in a format you can at least begin with, is a six month ordeal.
Having your hands on the pulse of billion dollar divisions is kind of cool. The six or eight layers of wankers you have to go through, to accomplish this -- not so much so.