Affordable place to say in Cassis & Villefranche-sur-Mer!!??

How do you define "affordable"? And what amenities do you require? Would you accept a private room in a hostel? Must the room have ensuite bathroom facilities, or a bathroom down the hall sufficient? Please provide as much detail as possible, so others can help you.

For what sort of dates are looking?

We stayed a night at the Hotel Liautaud in Cassis a few years ago solely because of its location right on the quai. It was an average hotel in a great location. Don't know if it has been upgraded since then but you should check it out. If you will be driving note that parking is problematic around the harbor with only a small paid lot across from the hotel.