Hire the hall a much better option and more cost effective.
We had 35 kids last week, I hired the church hall and had play dough out with dd cutters and things ( playdough was £2 in our half price shop)
Bought some fuzzy felt in our cheap stationers buy ine get one free (£2.00) again.
Bought a huge jewellry making set (half price in woolies £5)
Rolled out sheets of old wallpaper reverse side up for kids to doodle/draw on - free
Photocopied some disney pictures ( free dp did it at work)
Spent about £35 on art and craft stuff - ordered crowns, aprons, party bags from party pieces. Some cut out shapes from a mumsnetter, as well as glitter, material scraps, gummed shapes from our craft reject shop.
I also put up dd bouncy castle,her tents my mum and a friend did face painting and we set up a baby corner using dd old toys.
I did my own food ( cost me about £80 but I fed 35 kids and their parents and the food was amazing.
For party bags I just bought books from the book people, bought 40 for £20 and had some spares to give away as prizes for pass the parcel etc.
The party was much cheaper than a soft play option at £7 ahead and much much better. And I had loads of art and craft stuff left so i am halfy way to next years party.