We use F1 Motels quite a lot. They're as basic as it gets but very cheap, and if you just want somewhere to crash for eight hours they're fine. There's loads of them around, normally easily accessible from the autoroute.
Be aware that some of the really budget hotels don't have ensuite rooms. We stayed in a couple of budget places (1x IBIS, 1x other brand I can't remember) whilst crossing France last year and found the Ibis was worth the extra cost (but I was with the wife and toddler). The budget hotels often have the advantage that you can check in anytime with a credit card, but the disadvantage of being popular for knocking shops / group travel at weekends and consequently noisy.
It's worth looking at Chambres D'hote on tripadvisor or similar - prices are often reasonable, they're quieter and you get more of a French or unique experience.