Ferry
There are numerous English channel crossing points, from the Dover-Calais/Dunquirk route from as little as £20 each way, to a Plymouth-Santander mini cruise that in peak season can reach £800-1000. Your budget and starting location will determine the most cost effective route for you. It’s worth noting that some ferry companies will charge considerably more for a van than a campervan (or a van with windows), so get a few online quotes. Norfolk Line seems to charge a minimum of £100 each way for a van, but a motorhome gets the much cheaper car rate. Brittany Ferries who run the Plymouth-Roscoff/Santander routes don’t seem to discriminate against van drivers, the ferry journey is more expensive overall (due to crossing length) but can save a considerable amount of driving and have the added benefit of overnight crossings with very comfortable cabins to make the most of your annual leave!
Generally all the cross channel ferries seem to be comparable in terms of crossing length to cost, and it’s worth calculating the extra miles you may end up driving before booking the cheapest ferry. The Plymouth-Santander route is an expensive option with the cost far outweighing what it will cost to drive to Santander from Calais, for instance, but benefits by delivering you fully relaxed only 10 hours drive from Tarifa, Sagres, Guincho or Morroco!