Hey Mike, I rode west and then north through Paraguay before cutting back into Brazil at the obvious spot enroute to southern Pantanal. Worth thinking about if you don't need a visa (I did, but got it in B.A.). Nice folks, cheaper than Brazil, and not a lot of other overland riders--like none, in fact.
Don't know that there's any way to see the Pantanal cheaply, but definitely worth going. Do as many boat trips/walks/game drives as possible, and try your best to believe them when they tell you that these particular piranhas don't generally eat swimming humans.