It's pretty amazing how cheap that is.
For $720 million, they built a half-ton spacecraft, launched it into space, sent it on a path out of the solar system, tracked and guided it all the way, and had it gather about a million times more data than existed before about a particular small icy body billions of miles away.
To put it into perspective, that's about what it would cost to buy two A380 airliners. Two. You can buy two airliners that are not much different from the ones that existed 40 years ago, but that happen to be somewhat larger and carry some more people, and then have to spend even more money to operate them, or for the same money NASA can do an entire mission to Pluto from start to finish.
Or for a different perspective, for the cost of the B-2 program (an airplane which basically never had a mission, whose key feature probably doesn't work anymore, and which in any case is far too expensive and precious to risk in any environment where there's the slightest chance it could be shot down), assuming costs would be the same as Pluto, NASA could send seven missions each to every planet in the Solar System including Pluto.
For yet another perspective, it's about 1/9th the cost of the Washington Metro's Silver Line product. So, one mission each to every planet in the Solar system including Pluto, or 60 miles of railroad track and 11 light-rail stations.
It's not a sign that people aren't being taxed enough, it's a sign that NASA is a bastion of amazing efficiency and capability in a sea of unbelievable waste.