Rent a flat or a house in Languedoc Roussillon

Assuming you mean long term rental, rather than holiday rental, the position is not easy.

Firstly, most is unfurnished. Prices vary enormously by size, standard and location. Think of €10/m2 for an apartment in a small inland town. Cities and coast will be more, further north towards the Cevennes will be less.

French law protects the tenant, and it is almost impossible to evict a non paying tenant. Tenants who do pay have virtually lifetime security of tenure. This results in owners being ultra cautious, requiring employment contract (cdi required), salary slips, tax returns, bank statements etc. In many cases a guarantee is required even for adults if they can not produce the required documentation (i.e. in the probationary period of a new job, etc).

Most agents require this before they contact the owner and therefore it is difficult for foreigners to get rented accommodation. Owners who advertise in the press, leboncoin, etc and deal direct will need the same information and their lack of English makes negotiation on terms difficult. 

When I needed to rent for 3 months (waiting for my house completion) I paid deposit and 3 months rent in advance.

The easiest way is to search the expat websites for out of season  gites and apartments or property where the owner has returned to UK.

Unless you speak French and can provide French documentation:anglophone-direct.com and the-languedoc-page.com/phpBB2/forum and both take free "wanted" posts.

Peter