The area around Porte de Clignancourt is great for shopping. Flea markets and lots of antiques stores.
check first for market days, then go there and spend many hours browsing around, making great bargains!
What to buy: Anything from furniture to clothes, jewellry or books... Also, there are nice coffeehouses where you can have a break!
What to pay: As much as you want to. No limits any way!
The Clignancourt Flea Market is arguably Europe's largest, and stretches for blocks and blocks on the north side of the city just beyond the Périphérique, Paris's infamous "ring road".
What to buy: You can find absolutely anything here -- somewhere -- from 18th century antiques to African sculpture, and from old, worn-out toys to 19th century erotica. If you can imagine it, you can probably find it here.
What to pay: From nothing to thousands.
At the Vanves Fleamarket there are some record dealers.
BTW Thanks to ForestqueenNYC for the scouting and the pictures.
What to buy: Records
What to pay: Higher prices than average
The Vanves Fleamarket is less known than the Saint Ouen one in the North, but very worth a visit.
Open Saturday & Sunday 7AM to 11PM.
What to buy: Old stuff.