LAN Colombia has filed a $501 (bookable on Priceline.com) fare to the Iguazu Falls (Brazilian side).
I could not make the fare show on ITA Matrix myself, so you may need to use Priceline for date combinations.
I went to Iguazu Falls in December 2013 and had a blast. I stayed on the Argentinian side at the Sheraton Iguazu Falls and wrote a guide on how to best experience the falls from the Argentinian side of the Iguazu Falls.
The visa fee for a Brazil visa is currently $100 for 90 days. For Argentina, you have to pay the $160 reciprocity fee which is valid for 10 years (unlimited entry).