The best way to save money is to use Tesco Vouchers, got Eurotunnel for £20 in vouchers plus £4 this year. The vouchers can also be used on many of the ferry companies, some of the Dover crossings can be less than £40 return anyway if you pick the right crossings so that could work out a £10. There was a offer recently that gave you 1000 points (£10) when you bought a tesco phone (cheapest one was £15) so you actually got a phone and a return crossing for £15.