Just came back from Maun today myself. Drove up with friends but I know Air Botswana fly up there from Gaborone or Joburg.
You can take the Intercape bus from Joburg to Gaborone for R130 if that helps to keep costs down but not so convenient. Don't think there is a bus from Gabs to Maun though...
They expect you to camp over for a while but from what I understood January may be a bit late for recruiting.
Good luck!
Eric