I Need Help Budgeting My Around the World Trip?

I'm planning on starting in Hong Kong, going from their through South East Asia (Cambodia, Thailand) then to Nepal, then India, then to Sri Lanka, Madagascar, Tanzania, Kenya, and Morroco, before returning home to the US. I'm thinking this whole trip will take 5-6 months. I'm expecting to backpack, stay in cheap to medium hotels. How much do you think I should save for this trip?