I bought my kids a big bouncy castle last year cost me £200 secondhand but I have to tell you it was the best £200 I've spent, it got to the point were they were bringing there friends around and I had to put a stop to so many wanting to come around, I didn't mind the fact that so many kids were coming,
I just didn't want the responsibility for any injuries.
I told them I was going to charge them all a pound for using it and everyone said we'll pay :

I thought if I told them that they would stop coming around, how wrong you can be?
It has to be a good little business but not for me.