Hospitality exchange is an amazing way to travel without spending much money. You get to stay with locals, for free. And when you're home receiving guests is a bit like traveling yourself.
There's a funny history to hospitality exchange networks. The gist is this: CouchSurfing is now by far the biggest but is generally considered to be in decline (partly because it's now a for profit corporation). BeWelcome is a much smaller but growing nicely.