We have just wrapped up on a joint 3 year old birthday party at a children's museum and it came out to be $478 total. So since we split it comes to $239 per birthday boy. Here is a break down:

Children's museum, package deal 25 headcount total, including hosts and adults
Venue package price: $230
Cake + candles: $53
Card: DIY, $25 materials only
Veggie + fruit: $24
Favors, plates: $55
Pizza: $83
Drinks: $8

I am kinda suprised it was under $500 due to it being in the children's museum.

I am curious to know about how much did you spend on your parties, your venue, size (if you had 100 guests and did you hire ponies or magicians), and how did it break down!