As a massive fan of Earthbound, no, no, no no no no no.
The game is not worth $100. Over the years it's been artificially inflated by eBay retailers to the point where they're pretty damn overpriced. Just about a year ago you could find them for $60-$80, recently loose carts have begun regularly breaching the $100 barrier.
If you really, REALLY want a cart, I'd say buy one online as cheaply and as soon as possible, before prices get much higher. A much more sensible course of action would be to scour your local retro game shops, car boot sales, thrift stores, flea markets etc. and just hope to get lucky - you'll find a lot of 'miracle' stories out there. Compared to other truly rare games Earthbound carts are in abundance.
Same thing is happening is Mother 3 carts as well. Observe thine graph created this July: