A tea party could be beautiful and does not have to cost a lot. Use your best china, crystal, silver. Purchase beautiful, tulle and some silk flowers and use this as a runner down the dinning room table.
Make finger sandwiches and go to the best bakery in town and purchase miniature pastries.
You could deliver the invitation placed inside a pretty teacup and saucer to each girls home. Go to Ross or Tuesday morning to purchase the cups and saucers.
Ask the girls to dress up in their fanciest clothing... Take pictures and have your daughter print them out and then she can write her thank you notes on the back of the photos..
We once took a huge group to a beauty school and had them do "Updo's" on each girl it only costs $10. each, then we had them dress up and took them to a house where we served them a fancy dinner by candlelight.. They loved it.
Brunch is also a fancy way to serve them and does not costs as much. Purchase a Stacked cake and decorate it with fresh flowers to make it a little more formal.