I highly recommend thrifting, or op-shopping or whatever you want to call. It can be time-consuming but if you have a good eye, you’ll find something to use or change and always for a good price.
Last time I got an enormous blue velvet dress and a blue taffeta thing. For the velvet, I was thinking about a skirt but hello! It should be made into a jacket. It’s hardly the season but that only means I’ve got plenty of time. I wanted the taffeta to make into a skirt, as well, but I went to a Bond/Casino-themed party and it was a little bit Casino Royale, so I wore it.
Paired with a corsage from your thoughtful date and some grad cupcakes, you’re party ready! Now strike a pose.