I wouldn't. We did it one Christmas & I hated it.
Will it even be enjoyable with your son who has Autism?
I know it wouldn't with any of my family that have Autism because they are ALL very regimented eaters. One will not eat anything out that isn't pizza, which most places will hsppily do, but not on CD. 2of the others will not eat anything that touches another food, another not anything 'wet'. The list goes on.
however, I do have friends with Autism who are much more able to eat a wide variety of food and in that situation it's usually ME, that's altering the menu.
I'd rather have CD at home.
However, the question you asked was 'how much' I'd expect to oay £75 per head absolute minimum & no (autism aside) I don't think it's value for money, at all, especially if you pay under £150 per head, at that point it might be, but personally not paying £300 for 2 for CD.