I gather it's not only gowns they need but accessories too. Shoes, evening bags, etc. (Not sure why the laser focus on dresses - it's not inexpensive to rent traditionally male formalwear either.)
As I poke around a bit on the internet, I see a lot of groups finding ways to help with prom-related issues. Clothing, ticket expenses, safe after-prom experiences, and on it goes.
Little Mr. A's prom feels long ago and far away, because it was. Mr. A and I had been invited to the Kentucky Derby that year and we chose not to go so we could take photos and see off the handsome couple. Have never regretted that. (The horse we were invited to see did not qualify and a storm kept the private jet sitting on the tarmac for 4 hours.)
You never saw anyone as happy as Mr. A was to learn that he'd given up the correct event.