You can find a market almost every day in Provence ... you just have to know the right town for the right day. The Apt market is one of the largest and it only takes place every Saturday morning. You will find lots of colorful local produce , as well as local crafts such as lavender pouches, home-made linens, etc. Side street vendors are typically cheaper than the main street ones so make sure you shop around (for example, the same white linen dress is priced €29 on the side street vs €40). It’s ok to bargain with the vendors.
Try to go earlier in the morning when it’s less crowded. Merchants start to pack up at noon and by 2pm, the whole market is completely emptied out.