Congrats, Donna! You'll be stunning, whatever you decide to wear!
My youngest has had the best luck shopping at the Goodwill and Salvation Army stores recently: she has brought home at least 3 dresses for Homecoming/Prom and not paid more than $4 for any of them. Two were David's Bridal tags, and I don't recall the third that was so pretty. She had a lovely copper one that will be for her BF's Homecoming this fall ($3), a pretty golden egg-y yellow colored one that she wore for Prom ($4), and another one that was a pretty greenish-blue for $4. None had to be altered in any way .... yes, she was really lucky, but she LOVES shopping there. Finds terrific deals all the time.
And if you go this route, you can buy some nicer shoes for yourself. Just don't tell anyone how much your dress REALLY cost; they won't believe you 'cuz you'll look like a million $$!
Odessa