If you are invited to a party and bring a gift, I'd expect food to be included.
I agree, unless you are having a big crowd, or doing it at prime business time, not booking a party is SO much cheaper.
We did DD's party by just showing up, using coupons for food, drink, and tokens. I bought each kid a balloon, brought our own goodie bags and even brought our own cupcakes. They sell birthday cakes now though, so you can even buy a cake without booking a party. They sell little CEC goodie bags at the prize counter too.
I think the price of the party is crazy.
At our CEC, Chuck comes out every day, and they will play the birthday song if you request it. We usually have playgroup there once a month.