A couple of tips--
I have my budget for the party 13 months prior. So, for the 8th bday party, all the money is in place one month before the 7th bday. That way I can shop all year, and if something changes, I have a little wiggle room to dip to the next years budget. I shop all year long. One of my favorite things is to get things that are seasonal. I can pick up things that generally cost $8 per, for more like $0.88 at times (the beach roll up mats, for instance, that I grabbed yesterday).
I think in general themes. DS#1 wants a Pirates of the Caribean party this year, well, I've always figured somehwere we'd have a pirate party. So much can go to it. Anything with pirates, ships, luau. I'll be going to Target to grab some Halloween items the day after that can go into a pinata for a pirate theme. Those packages of 40 that are selling for $5 will be selling for $0.20 Nov. 1. Also, grab things that aren't party theme specific. What theme does glowsticks not go with?
Always look at the clearance items at
Walmart (last year I got those really nice Darth Vadar masks that sell for $3 each at $0.07 each--every kid got one for less than $1), Target (clearance & dollar spot), Dollar stores, Half price book stores (I'll frequently score coloring books, simple readers, or comic books for $0.25 each--and they are the very nice ones, seen at Walmart for ~$6 each), Big Lots, Tuesday Morning, outlet stores (card, party, toy), clearance & sales at party supply stores, Oriental Trading (google for coupons), US Toys (An Oriental Trading type of thing), professional supplies stores. Heck, I grabbed some stuff yesterday at our upscale toy store out of the bargain bins--expensive things at dollar store prices. Also look for things that come in packs. At the dollar store I grabbed a package of stickers, 10 sheets to a pack, and the sheets were huge and packed with stickers.
I recylce things from past parties. I never throw things away. Especially things that are party favor leftovers. When DS#1 turned 1, his party favor bags were nothing but left overs from the olders ones parties. They were all a bit different, but the kids got them as they left, so they don't know anything. I have a great supply of cake pans (always do the cake myself, taste better than grocery store cakes and is a heck of a lot less expensive than a bakery)--bought inexpensively, just $2 or $3 dollars, from ebay--that can be retooled into other things. The Wilton website is great for letting you know how. I have a dinosaur cake pan that has also been used to make a giraffe cake for the jungle theme party.
I also do other things myself. I make the pinata myself. The same ones that would cost $30+ in the stores, cost me less than $5 to do myself. The internet is a great tool for that. And, buying clearance candy after Halloween is a great way to save money there. I fill that thing so that every child can pack their bag (or whatever I hand out) full of pinata and candy toys and still have some stuff left over and usually spend way less than $10. Small toys are the best things to put in pinatas because they never go bad. Watch for those party packs of playdough to go on sale. And never underestimate the multipurposeness of the plain lunch bag.
If you are going offsite, look for the value in the place. I won't do a Pump It Up Party because I'm cheap. All you get is the site. Another party place around her cost the same price, but they include themed invitations, and themed plates, themed napkins, themed cups, party favors (although I add to it), balloons (mylar), unlimited food & drinks for an unlimited amount of adults, unlimited drinks & a meal for the kids (5 more than Pump It Up includes, & then charge less per extra child), & themed cake (enough to feed everyone), and two party hosts to handle everything--they even take the pictures & print you digital copies (2 sets) before you leave. Plus, the have 3 different party rooms that cater to a wide variety of themes and one blank room that they decorate to your theme. It is just as fun as Pump It Up, and not as exhausting half way through the party. Plus, it is run where you play, eat a meal, play, have cake, play, open presents, play, pinata, play, goody bags & go home. The kids LOVE this.
Bigger places (especially chains) will run coupons, you just have to look for them. And, ask for discounts. You'd be amazed at how often you can get them. Ok, you might have to have the party in an off time, but really a Tuesday evening b-day party can be a lot less competitive than a Saturday afternoon party with kids schedules.
OK, that is all I have time for now. Must go to the baseball game.