You can now book for 2017 on the Newhaven-Dieppe ferry. 4 hours on 2 modern but basic ferries. Just checked and these prices are available during school holidays also. They will go up in price quickly in my experience. £49 each way is based on car +2. Goes up a little for extra passengers.
Ignore the bit where it says you can only book up to Jan 5th 2016- all 2017 now possible. I use this route to France to avoid the nightmare at Calais!!
From DFDS website
NEWHAVEN–DIEPPE FERRY CROSSINGS
Hop across the Channel from Newhaven to Dieppe, in the heart of Normandy with our short, 4-hour ferry crossing. It’s the perfect way to explore western France or even head to Paris!
Also Golden Oldies Over 60's if you go to Newhaven Ferry terminal or ring them up you can get another 20% off- not available online- valid ID needed.