S.H.
please don't overspend. It can create issues on down the line for the "other mothers", & at times is off-putting to the teacher too. Just saying....been there, seen it happen, & the after-effect was not optimal. :)
Use your own creativity & exuberance to make this special for the kids. As with most life lessons, from the heart is much better than from the wallet.
There are 2 websites which are my go-to resources for parties: Family Fun & Better Homes/Gardens. Occasionally, Martha Stewart too. Please try to limit the amount of sugar, please try to think of the kids with issues who do not respond well to over-stimuli. All of this factors into a GREAT PARTY!
Been throwing parties for years now....I find it's always best to pick a theme or aspect, & build the party from there. Since you're working with 1st/2nd grade, I would recommend staying away from the songs or anything which would mean that a handful of kids wouldn't be able to keep up with the group. (unless you know for sure that all kids in the class are on the same track developmentally.)
Good luck & kudos to you! & here's the website for Family Fun: http://familyfun.go.com. I did check it out & there are some awesome ideas!