I suspect that you might get one cheaper in a backstreet army surplus place, but if you click on
http://www.silvermans.co.uk/Silver/docs/topframe.htm and enter "parachute" in search - I just found green cargo chutes at £200 each and 3 colours of life-ex personal parachute canopies for £150 each.
I have met parachute games before when I used to be a scout leader, much fun to be had !
G