The Inspector wrote:
$16.75 Million EACH!

for that kind of money you can pick up a used 737-300.
Apples and oranges though. Each Super Tucano will come with the airplane, parts, and support for the next 10+ years included (depending on the exact wording of the contract, but that's pretty standard for DoD procurement). It usually also includes the manufacturer training your initial cadre of instructors as well in that cost. With the 737-300, you get the plane. That's it. No spares, no support from Boeing, no training for your mechanics and crews.
That's one of the things I really do hate about DoD procurement. They amortize so many costs into the "per aircraft" price that you really don't know how much the plane itself costs and whether the DoD is getting a good deal. You have to wade through thousands of pages of information to finally find what it costs for the airframe and equipment onboard only, and then you have to figure out if that includes cost of GFE like the engine, avionics, and pyro or not.
I once dug through the F-15E initial build contract award (back in the late 1990's and yes, I had no life as a teenager... in fact, I really still don't have one

). The widely reported number was that each F-15E cost the USAF ~$50 million in FY1990 dollars. When I broke it down, I think the actual airframe, non-classified avionics (i.e. the stuff MacDac actually bought to put on the plane), and engines (which were a separate contract) came out to like $15 million a copy and all the ancilliary stuff (manufacturer support, spares for that airframe, amortized development costs, etc) made up the other $35 million. Now, that contract was supposed to cover all the non-GFE equipment purchasing requirements for the first 10 years of the airframe including quantitative spare parts (i.e. the ones you know you'll need every "x" hours/years of service), overhaul and maintenance at the depot and manufacturer level of certain structures by the manufacturer, manufacturer on-site support (aka AOG), and document support (i.e. flight/maintenance manual updates).
When you think about it, those prices aren't too unreasonable for an airplane that is capable of doing almost 3 times as much as a single B-17 was in WWII and which (in FY1990 dollars) cost ~$2.5 million per copy.