Hi there. I doubt you will get any cheaper than via atm. Not directly connected, but you might want to have a second method of accessing cash eg. some preloaded via western union or similar.
Beautiful country for sure - but most definitely the most dangerous place I have travelled - spent a month there a few years back. Watch your back at all times. I was told on a number of occasions to get out of dodge in Bogota. Cali is even more hardcore.