How much should I save to backpack South America for 60 days?

I am planning on leaving Jan '10 for a two month (at least) backpacking trip starting in Lima, Peru. I hope to visit (in this order) Peru, Bolivia, Chile, Argentina, and Brazil. uming I am very tight with my money (hostels, cheap meals, busses, etc.), how much will I need for this trip (not including airfare)? I know this is a hard question to answer, but reasonable estimates would be much appreciated. Any other tips/pointers would be very appreciated as well. Thank you!