A.H.
I think a park is great, I'd rather take my kid there than to be confined in chucky cheese! :)
You might want to locally price comp but I know Party City has their toy story supplies 50% off. So you're in luck! If you plan on doing the goody bags I know a lot of people who use orientaltrading.com, they have pretty cheap prices on decorations and fillers.
I was also a little strapped for cash for my son's birthday and ended up mix matching themed things and clear utensils/plates/cups so we could reuse them for other events. I also made the cake myself to cut more expenses, cupcakes are much easier and they have really cute toy story 3 decorations for them.