I'm a conworlder, That's pretty much similar to a writer, but instead of writing novels I like to create the background stuff.
I write short storys too, but often catch myself in outlaying, in which was the culture of the characters is different than ours, and what effect that has on their dayly lifes.
What I like about this hobby is it's diversity. I think I would never have become interested in the different features of estuaries, if not for this.
Not expensives in terms of money, most information can be found in the internet for free, but it can be very time consuming. Just try writing a poem in a language you invented yourself.