Costs 

The all inclusive costs of an 18 day trek in Tsum and around Manaslu with guide and one porter is around 1100 $ per person for a group of two, or 900 $ per person for a group of three people. 
All in all, an average total, all inclusive cost of 60 $ per person per day is a fair guesstimation, to be tuned to individual luxury tastes.

Once you have paid for your guides and permits, it is probably best to bring along enough Nepalese rupees for a 30 to 40 $/per person per day expenses budget, covering food, sleep, snacks, drinks, tips, transport and whatever else takes your fancy.. This is excessive, but it is best to be on the safe side as there are no money changing facilities anywhere outside of Kathmandu or Pokhara.

The Nepalese rupee exchange rate is around 100 for 1 US $ 

The following table is an approximation.