In a replay of events of the 1982 Falklands war*, a $285 million South African Type 209 class diesel-electric submarine "avoided efforts by surface ships and aircraft to detect it, and proceeded to "destroy" several NATO ships" in joint South African-NATO exercises. This sub, at 1300 tons displacement, is about a fifth the size of American nuclear attack submarines is, at least, a third the price.
Once again, the submariners motto that there are only two kinds of naval assets, submarines and targets, seems to have been proven true. The other major examples in involve two Department of Defense war games, one designed to replicate an Iranian attack on a U.S. fleet in the Persian Gulf that involved major losses to the surface fleet, and there other of a World War III scenario in the Atlantic that predicted that surface fleets would be quickly vanquished.
* According to Wikipedia (and widely discussed in military analysis):
[M]ilitary historian Sir John Keegan noted that the brief conflict showed the irremediable vulnerability of surface ships to anti-ship missiles, and, most importantly, to submarines. Thus, despite the seemingly limited consequences of the war, it, in fact, confirmed the dominance of the submarine in naval warfare. This is especially so, Keegan argues, because submarines are far less vulnerable than aircraft to counterattack, being able to approach and destroy their targets with almost complete impunity.
The only other time a submarine has actually made a kill since World War II was when the PNS Hangor, a diesel electric submarine, did so during the Indo-Pakistan War of 1971.
Both China and North Korea have large submarine fleets.