I had a little party for my daughter this past summer. I too was on a tight budget. I had some water games planned out but it rained so we were stuck in the basement!
Instead, I did a little spoon race...ping pong ball in place of an egg. The kids LOVED this. I don't know why but they thought it was totally funny. There was no pirze given just bragging rights. I divided them into teams an let them go around the "track".
I also had some of those giant balloons at the end of rubberbands (dollar store 3 or 4 to a pack) that kept them busy the whole party. We took a brake for pizza. I also had little snacks on the table for them.
You could do a little scavenger hunt to find their goodie bags.
When it was time for their cake I had them sing and did the whole candle thing. Then I had them play a musical pass the ball game while cake was being cut and plated. Each time one of them was out they got to go sit at the table and wait for their cake.
Then we did gifts and they went back to those silly balloons!
I had kids there from age 2 up to 11 and they all had a good time. I was actually suprised they had so much fun!
Our party was longer than an hour so you probably won't need to do that much. The dollar store or Walmart usually has great party toys/games. I got one of those pin the nose on the clown game. I even played w/them...they loved that! We spun each kid the number age they were (i fell over a few times while spinning). I would have oldest go first (they feel for where the other stickers are!)
Hope this helped, have fun!