I'd say go look at the fabric store in the pattern books. I'd recommend almost any short dress in the "formal" section of those books.
I always steered clear from wearing white, black, or red to a wedding. It is just something my mother droned into my head. However, if it is an evening wedding, the "little black dress" can be a fabulous choice - so I ignore Mom's advice on the black.
You also might look into some of your local thrift stores. I bought a totally sequined dress for $13. I was going to wear it to my 25th high school reunion, but now found out we are only having a cocktail hour/dinner, not a formal dance.
And don't forget about Ross/Marshall's/TJMaxx. You can get some GREAT looking dresses for great prices (but you have to go back over time).
Get an idea of what style you are looking for first, if you decide to look in the thrift stores or R/M/TJM.
Good luck and let us know what you decide!