Flower girl

Back when department stores (i.e. Zellers, Sears) were still a thing, I bought dresses at places like those for school dances/family gatherings. I also walked by the Children's Place in my mall and they have lots of cute dresses for girls that would make nice flower girl dresses. These places will definitely save you some $$$ and no one is going to know you didn't get the dress at a bridal place.

Also try looking at places that sell First Communion dresses, if that's more the style you're looking for.

I'd definitely try and catch the post-holiday sales at the department stores.

I didn't have a flower girl, but when my cousin did a few years ago, she got the dress at David's Bridal.

Honestly, if you're not wanting to break the bank, I'd just look in the party dress sections of places like The Bay. Otherwise I'd check out David's Bridal, or other bridal salons.

I bought mine online at Hudson's Bay just after Christmas. You might still be able to find good deals on post-holiday party dresses. The best advice I got from someone was to look at children's clothing stores instead of bridal. Saved me a bucket of cash!