I was very lucky and found Earthbound for $5 at a thrift store about 3-years ago. Having been collecting for several years prior to this I was well aware of this games status as somewhat of the "holy grail" of SNES collection. Given such an illustrious title I had very high expectations regarding this game. Sadly, I was very, VERY disappointed.
The graphics are below average, the music is meh most of the time, the gameplay is bland, boring and repetitive, and the story/characters are fairly uninteresting as well. The quirkiness of this game was lost on me and it never really inspired me to want to continue playing at anytime. Needless to say, that is my assessment of the game, but I still couldn't help but wonder where in the hell all the hype came from towards this game.
My theory is that a relatively small group of people who played this around the time it came out probably liked it for a variety of reasons to the point where they remembered this game years later being way better than it actually was. I'm guilty of doing this myself with various games. Then comes the internet and all they can say on every forum is how amazing this game is and it is one of the best games on the SNES, driving people into believing it is really that good.
But to answer your question, Earthbound is an SNES RPG, I'd consider it to be uncommon (not to be confused with rare), and it is a fairly unique game, all reasons why it would have an inflated price. However stacked against games like FF2, FF3, Chrono Trigger, Breath of Fire, and Super Mario RPG, all games that are objectively better and chapter than Earthbound, I can't justify this game being worth more than $60, tops.