you should be able to live on the cheap for say 400-500 bucks a month. thats including a tent stay at audi camp which i think comes to 110 or so per month ( double check ) and then just money for food at around 10 bucks a day plus transport which is cheap.
but thats pretty much slumming it out if you do that. the thing you will find about southern africa is that none of it is nearly as cheap as you may first think.
keep in mind too that during my 3 month tour in maun I was "housesitting" for about 85% of the time but thats just because I'm the man and people like me
