T.P.
You might check into Libby Lou in Arden Fair Mall. Good activies for this age group.
Play in the park near you.
Get dress up clothes from thrift stores.
Have the girls come dressed in there favorite dress-up outfit.
Make necklaces, T-shirts, or other clothes related items. Get ideas from Michael's.
Make sure with that many kids you have some more adults around to help you. Rule of thumb is 1 adult for 6 kids. That way the amount of kids does not become overwhelming and control can be maintained especially if someone or something happens that requires all of an adults attention.
If you need any other ideas feel free to contact me as I have done budget friendly kid parties for over 15 years.
____@____.com.