Barbie, if you have any friends or acquaintances about your size, check with them to see if they might have a dress you can borrow. Even if they aren't your size, check around anyway - maybe they have children or relatives close to your size.
I am a bit of s skinflint, I don't like to part with $$The Big Bucks$$ unless or until it is for something I really want or need. A high-priced, probably-wear-it-once-then-never-again, dress was definitely
not in that category, even when my daughter announced she was getting married.
I hemmed and hawed for a bit, and ended up borrowing a very nice, very suitable dress (with a matching jacket, no less!) from a close friend who used to maintain a small costume collection! The dress was lovely, I was well-dressed for the event, no one knew the difference. I had the dress and jacket dry-cleaned after the wedding, and returned it to my friend.
No one was the wiser!! I even got several compliments on "my" dress.
Anne