Bigarse, have you seen the Bilbo thing that everyone was talking about much earlier? I only just looked at it and think it might be great for my autistic child. I am also planning on getting a very fluffy cushion from Ikea, a balance board, a soft rug, and an Infinity Light from Argos. (For underneath a midsleeper bed, which already has some beanbag style cushions from Tiger and a little fibre optic thing from Tiger, which was cheap and she loves.) Really recommend Tiger for random cheap sensory things if you have one to pop into occasionally.
We also have a gorilla gym, which is a swing/ladder/monkey bar set that you can really easily attach to a door frame. It's brilliant, but not cheap, about 120, I think.