R.C.
This was around the age that I started having sleepovers for my daughter's birthday. You can keep the cost down by putting a limit on the guest list (sometimes hard to do though because you want to avoid hurt feelings and all). Also by serving hot dogs, (pancakes in the morning), baking the cake yourself and buying decorations and party gifts at the dollar store you can have a great party for your daughter without breaking the bank. Be careful about cliques though, girls have a tendency to form small groups that leave others out. I once had a rather large sleepover for my daughter and to avoid this as much as I could, I let them know right away that I would not tolerate that behavior. I also had a lot of games/activities planned for them that kept them busy and doing things as a group. It was a great success. If you need any ideas for party games/activities, here is a website I have used: http://www.partygamecentral.com/
Feel free to contact me if you have any questions. I hope this is has been helpful. God bless!