I have been playing Pokemon in some capacity since it was released, I was never a fanatic but I have always enjoyed it.  The main reason I am playing is my girlfriend also enjoys the game and we went on a long walk today to play together, it was really nice.  Taking over a gym together was a relationship bonding experience.
We haven't spent any money yet and we both have so many items because we walked around a lot and got a lot of free stuff.  If you live in a city you will never need to spend a cent, if you live in the country you might not be able to find enough pokestops for free stuff.