Used to be part of a school group that decorated the local high school for the weekend into a "haunted high school". Considering that most of what we did was extremely cheap materials (think cardboard, duct tape, paint, plastic cloth, etc...) AND we didn't have to worry about building physical walls, yet we still ended up spending several hundred dollars (I don't know exact figures, but I estimate $600+), trying to get something done in under 100 pounds is... not going to work. Furthermore, the time investment involved is STAGGERING. We had over 60 people who put in over 12 hours EACH setting this up. One person is not going to be able to do this by themselves, let alone in any reasonable amount of time.
If you don't have any structural supports of any kind, you'll need wood and such to actually build walls, which is not that cheap. Plus, if you're doing this "professionally", you will not be able to simply use cardboard/duct tape/paint, but will likely need more substantial materials, which are also more expensive. In short, there's zero way you could pull this off with 100 pounds, and even with a substantial budget absolutely zero way you could pull this off in a fortnight.