Ok so you're paying £8.26 plus postage for an empty bean bag - but its a massive outdoor water resistant bean bag!!
Plain lazy recommend you buy the polystyrene balls from custompac.com - but dunelm also sell balls at £7.99 a bag (you'll need 4) http://www.dunelm-mill.com/shop/bean-bag-refill-47342
Factoring all this into account:
bean bag: £11.26 (with postage)
polystyrene balls (£7.99 x 4 = 31.96)
This is considerably cheaper than you can buy this size waterproof bean bag for!!
FRDLVRY for free delivery as well & 5% quidco
I had to add my address select shipping method (1st class) then go back a stage and add the voucher. As it said not valid initally, as there was no p&p added to the basket at the first stage... I was checking out as a guest
So can be had for £8.26 all in.. not £11.26 might want to amend the total OP