Shopping for prom dress in Paris

My granddaughters really enjoyed shopping for unique dressy to casual clothing in the Marais in 2019. They found some stores with individually priced items and others that were priced by kilo.

https://www.doitinparis.com/en/brownie-shop-paris-26066

Samaritaine, the hulking palace of fashion in the centre of Paris, has undergone a flashy and no doubt expensive facelift. Now it shelters many fashion boutiques whose famous names all add up to money. Worth seeing for the interior design's worship of art deco.
But for a student, some of the frocks could cost half a year's tuition. More fashion-aware minds than mine might know of second-hand bargains but I doubt that the trends are that much different than back home. Accessories, though, could offer more distinction added to the souvenir value. I always get a good scarf to wear three seasons a year.

https://www.dfs.com/en/samaritaine/

You won't find a "prom dress" those fluffy crinoline and net things we used to wear with the offered wrist corsage, a wedding dress-in-waiting, but you'll certainly find an interesting dress, or something creative, to wear to a prom. The prom-goers are so much more liberated and expressive today. Have fun.