The Southampton ferry to Santander for peds with a bike is £60 each way (no cabin) but weather in Northern Spain at that time of year not really good enough. Hiring a villa for 8 people in Santander bay for a week varies but around £100 each. Bay of Biscay could be interesting for passengers at that time of year. Barcelona slightly better weather but could also get a little interesting over the next few months! mmmm
Malaga is, apparently, one of the warmest winter locations outside of the Canaries with hostels around the £14 a night mark. Hiring a Brompton for a week is around £70.