At least I didn't start it this time.How about "complete waste of taxpayers money"?
However, in the realm of money saving, it's much cheaper than a brand new aircraft (a no brainer). Also, it will be integrated in the production line with the rest of the 737s for the most part. As I recall, it's competitor was an upgraded P-3, so the saving's weren't as big in the final selection.
While it is a big change to take a civilian airliner and bring it up to MilSpecs, the fact that the 737 has a proven record for 30-40+ years doesn't hurt it.
Those are the biggest structural changes are just beefing up some structure here and there and adding a weapons bay and wing pylons (and a million sensors, fairings, antennas, etc).