my DD went to one last week- they set $25 per child to spend- so the kids got a reasonable bear and an outfit to take home.
afterwards the party hosts shouted the kids mc donalds in the food court- she had like 12 people at her party so it aint a cheap party.
personally if she is interested in build a bear- then when not take her and a couple of friends to build a bear privately and that way you dont have to worry about minimum numbers etc.
Btw it was a 10th birthday party she went to