Budget for South America

I appreciate that this is a very general question but I just want to get a rough idea so that I can get realistic about how far our money is going to go. We are going to South America in June 2007, we are hopeing to travel for approimatly six months through the likes of Venezuela, Ecuador, Peru, Bolivia and Brazil. We are more then happy to live in basic accommodation and travel on the cheap but we do want to get a fair bit of diving in. We have budgeted around £3000, is this realistic or just plain silly.