The wilco cat litter is £1.79 for 5 litres and £4.25 for 15 litres.
I have been using the same cat litter, I get 1 hours viable cooking time with a single filling of 1/2kg of pellets.
The new pot stand is a bit loose when assembled, but if you squeeze the two open ends down a bit with pliers they click into place and hold well, I have cooked using a 2.5ltre tatonka kettle and frying pan which is 200ml wide without any stability issues. If you need extra stability you can also pin the cooker to the ground by pushing tent pegs through the lower air intake holes at a 45 degree angle.