That low total payload and cost were what turned me off of the Ramjet, and once you hit Lancer missiles, I don't really see any reason to use it. Although, I guess that's the point of it being an early interception weapon on the black market - best of a few crappy choices, fence it once you can start producing better stuff.
By the way, I love the Naval Gun on the Swordfish for brutalizing nonmilitary targets - I know missiles and light cannons are a better and more economical choice, but there's something satisfying about mounting an a WWII-era battleship Abrams tank cannon on an interceptor and slamming UFOs with 120 mm shells.
Edit: Got my cannon sizes mixed up, thanks for noticing my mistake legionof1