Birthday party for a 4 year old

Noah is to turn 4 in February which in the log scheme of things, not very far away! My question to you is, if I were to have a party for him this year with his friends, how many is a nice number to invite? And how much do ou recon it would cost? Food, bouncy castle etc? Anyone any ideas? I've never done it before!! We can hire out our church's hall pretty cheaply so the venue isn't an issue!

You probably wouldn't want to go with too many. Setting a very top limit of 20 would be best bet.

Of course, bar a couple of birthday parties for my brother, my only point of reference are brownies and guides.

I have yet to be able to throw a kids party for under about $200- Even the simple small gatherings end up being about that much- I can say from past experiences that I found bounce houses to be the best bang for your buck! They love them, bounce all day and sleep like little angels that night! lol Just be sure to stick to the no bouncing right after eating rule, otherwise it cuts the party very short when someone barfs in there