The Pentagon part of the USN apparently overestimates what is necessary. Small, say 110-130’ advanced fiber boats with the 30mm Bushmasters, Harpoons and Stingers, with assorted small arms (Mk19, M2) would fill the bill very well and would be cheap. All the technology exists. Hulls exist already manufactured by civilian companies. The Admirals definitely need to get out of bed with the contractors and fill the void with an affordable vessel.
The catch is there is really no one size fits all solution here. The solution you mentioned might not have the endurance that an OPV or a coast guard cutter might have. If all you want to do is fight terrorists, insurgents and pirates, Harpoons are a waste.