With so much choice out there today, it is best to be slightly more flexible when choosing a departure city when looking into getting a ferry from England to France. You could get a hugely reduced price in the next port over, and if you are taking the car along, you have the added bonus of already having a mode of transport to get there.
With P&O ferries, perhaps the most well-known and therefore popular, you are restricted to just one port but it can be one of the cheapest options. Take for example if you were to depart on Saturday 17th September for one week, from Dover to Calais, for two adults with a car - this comes in at just £100. Check out poferries.com for more information.
If however you were looking to depart from Portsmouth, Brittany Ferries is a more expensive choice, but perhaps more luxurious and a higher standard. Departing for St Malo on the same dates as above, departing at an earlier time of 10.30am and also including a two berth cabin inside the cruiser including ensuite facilite, the price is a little over £400. Definitely a huge jump from P&O but this includes an overnight cruise to your destination, take a look at brittany-ferries.co.uk to see if it is right for you.
And lastly, the cheapest option of all, is the Dover to Dunkirk route with Norfolk line. Departing on a weekend away beginning on Friday 16th and returning on the Monday, for two adults travelling with a car, the price is a low £54. With only a two hour travel time this is a huge reason to get away from it all! Check out norfolkline.com to find a date that suits you.