I would suggest the chain hotels Formule 1 (which does not have an ensuite bathroom) and Etap (which does). You could also try Ibis and Campanile Hotels. These all can be booked over the web, but you'll have to put the names into a search engine to get their sites (I can't remember whether they are .com or .fr!).

http://www.villages-hotel.com is another. Family of four in one room with en-suite and breakfast about £40. Check the hotel for family rooms as some only have 3 sharing, not 4, if this is relevent.

Here's a good one to try

http://www.etaphotel.com/gb/home/index.shtml

One thing I find though is that I'm after booking a room in early September but you can only book up to May. Is this normal and is there anyway I can book a room later on in the year.
Thanks for the info about Formule1 not being en-suite.

Cols

We have stayed in many Campanille hotels, all ok and identical but not usually in the most appealling locations. In recent years we've looked for B & B's often providing evening meal. After a long drive it's nice to not have to go looking for a restaurant. We find this a better alternative.

Search the internet or look on ownersdirect web site

This is going to sound slightly corny
take a tent
find the MUNICPAL camping sites on your route and camp out some are as cheap as 5€ a night usual is around 10€ (£7) for a pitch not per person