I don't know if you would consider a party at home or not, but when my son was about 4 or 5, we had a space party at home. We cleared most everything out of the garage and hung glow in the dark stars and planets. We gave out glow in the dark swords and stuff from the dollar store. I bought a few black light bulbs from the dollar store and used them in the garage, so it would not be totally black. We played several glow in the dark games, like pin the planet on the solar system, glow in the dark tag, etc. We have a large backyard and the boys enjoyed just playing in the back yard. We had a large refrigerator box that we made into a space ship. We have a trampoline, so they enjoyed jumping on the trampoline, especially with lots of cheap balloons. We also had made our own pinata of a space alien head, using paper mache and a balloon.
There are a couple of websites that have party ideas, I think one is amazingmoms.com. I also have found great stuff, like glow in the dark slime kits, from stevespanglerscience.com.
I know that most people don't want to go to the bother of hosting a party at home, but my sons and I have always enjoyed planning and preparing for the party all most as much as having the party. It is a lot of work and I don't know that I end up saving much money, since we do so many cool things, but they are truly memorable parties. Sometimes we have rented a bounce house, but the kids really enjoyed just playing in our back yard. They LOVE water balloons, silly string, party poppers, too. It seems to be a more personal party and the kids actually spend more time together than when you go to a big "party" place like Chuck E. Cheese, where there are so many kids.
