Vintage shopping help!

Visiting for my 30th (f) in April and I’m a HUGE vintage shopper from the states. Almost everything I own is second-hand. The highlight of the trip is flea market strolling and, hopefully, finding one lifetime piece. Specifically seeking a black leather daily purse, vintage/second-hand, up to $500 (or the equivalent in euros, of course). I need to keep enough “fun money” to eat, drink, buy from flea markets, and get souvenirs (yes I will be getting an embossed hairbrush), but can be flexible with the bigger purchase. I’m staying in the Marais but we’ll cover all of Paris throughout the week. Suggestions, for stores or even bags you love?