Well, there are a LOT of things on
Talbot's website that would suit your price range and the occasion. You might want to check out the "Wedding Indecision" thread--some of the stuff I had linked to in there might be like what you are wanting. The 18-year-old wedding guest felt they were too old for her, but they would certainly not be wrong for a 27-28-year-old.
Most of the major department stores, like Macey's and Nordstrom's will probably have a similar selection in that price range.
I might go to my 10 year reunion next year, but I had a reputation in highschool for outrageous fashion and that part of me hasn't changed, so I will probably just drag something mad out of my closet and call it good.
Something like this with stripey black tights and my big Docs
or this, with spiderweb fishnets and my big Docs
or
This skirt and some summery top.
These are the sorts of things
I might wear, but I never claimed to have good sense or good taste. It all depends on your personal style and what you feel comfortable and confident in, and what kind of image of yourself you want to project.
If I went (and this is a BIG if, as there are still people from my school I wouldn't spit on to put them out if they were on fire) I would want my clothing to help me say, "I was weird back then, and I'm even
weirder now and having a damn good time, so suck on that ya' chumps!"