When throwing big parties you always have to look for ways to save so that it doesn't get out of control, but at the same time still have fun with it. Here are some of the things I've done to save:
1. Make your own food instead of buying or catering. Huge sub sandwichs cost about $10 a foot. You can make your own for much less then that. Think about all the food you can save money on by making your own for the party. Or you could even have the guests bring a small dish for a pot-luck type party.
2. Make your own party signs instead of paying for them. If you want a huge sign that says "Congradulations" or "Happy Birthday", why not make your own. Ask around and I'm sure you have a big role of paper somewhere that you can write and decorate as you desire. Get the kids involved.
3. Don't waste money on invitations. Make them on the computer for free. It will cost a little bit to print but you could always email them out too.
4. When choosing a theme for the party think of the colors that go along with it. For instance I threw a Superman party for my son. Instead of buying Superman plates, napkins, etc. I bought red plates and blue napkins. Much cheaper! (Plus any left overs can be used for other parties very easily) Try to do everything in the colors of theme and only choose a few specific items like a big Superman poster to hang up.
5. Think of unique themes for parties that will save you money. For instance I threw a Coors Light party for my mom and Uncle (twins). Most of my decorations were free because I used Coors light boxes and cans. You can do this with sodas or other items you can find lots of that someone really likes. They will have no idea they always wanted a "Cherry Coke Party" :-)
6. For party favors, buy items in bulk that are generic and decorate them yourself. I bought a big pack of lighters on ebay for $6.00 and put Nascar bandaids on them for a party I threw. Very cheap party favor that everyone loved. Everyone thought I bought Nascar lighters. That would have been expensive!
7. One of the easiest and cheapest ways to decorate is with streamers. You can buy a huge roll for about 0.79. You can do practically anything with this stuff and it always looks neat.
8. If you have a swimming pool you could fill it up with balloons. That's a cheap decoration that will probably get the most use. Kids love swimming with balloons!
9. Buy party decorations at garage sales. At almost every garage sale I go to I see party decorations of some sort. Add it to your collection of party stuff at home and see what you can come up with.
10. Share some your ideas!
Thanks, keep saving. :-)