Yeaaaah, hmm
.
There are so many disadvantages to going down to Spain this way that people don't put a price on.
Having driven that route on occasion in a car in the old days, I have been cured of ever doing it on a bike. It may"look" cheaper on paper, but it actually isn't in the end, and could potentially end up costing you much more if you trigger one or more of the 4500+ speed traps to be found in France along the way, which, by the way, your SATNAV is prohibitted from pinpointing for you other than to warn you that you are in the "general area" of one. That alone, however, may not save you because France employs private companies in unmarked cars to catch you as well. We all know, don't we, how well that works in the clamping industry in the UK!
If you are using the ride down through France as part of the tour and enjoying the sights France has to offer over a few days, then maybe, but blasting down over two days of hard (nervous) riding leaves you ill prepared to enjoy the freer Spanish roads. You may like "ironbutt" rides. That's fine, as long as you know what you're letting yourself in for. Certainly, if you only have a week, then similarly, you will be shattered by the time you have to roll in to work.
A return ferry to Spain can cost as little as £300 return without a cabin, depending on dates, both of which are what ramp up the price. A company of four can get one cabin and share the expense if you don't like the "(un)comfort" seat. Sleeping in a tent or a cheap flea-ridden hostel is not going to give most people a better quality night's sleep than one or two nights in a "(un)comfort" seat. More expensive accommodation narrows the price gap more.
Fuel prices have always been steep in France, and at the moment they are positively North Face Everestian!
Your tyres will suffer
a lot of W&T, especially if you risk a "spiritted" ride through France with the attendant higher fuel burn. It's a 1500 mile return journey, which, taking an average of 250 miles from a 20L tank, is four tankfulls (through France) @ €2/L = €160. You still have to pay for accommodation for a minimum of two nights (rtn).
Your tyres will flatspot, especially if you are carrying luggage, and especially because most UK riders can't corner for toffee.
. I hasten to add that it's not through lack of ability; more lack of practice and playgrounds.
If you add this all up, the balance comes to barely £200 of saving. That's assuming no fines along the way, of course, and you do arrive in far better condition to learn to corner
, and to return to work afterwards on the ferry.I understand that £200 is a lot of money to some people but, as I say, just one speeding fine could wipe most (or more) of that out.
So, to conclude: Dieppe route
£100 Ferry (rtn)
£150 Fuel
£80 Accommodation (rtn) on the cheap ( I appreciate happy campers will pay about €15. Good luck with the next day's 8hrs in the saddle.
£50 (BF, Lunch + dinner x2 adjusted for what you would spend on the ferry anyway)
Total €380. (Not including W & T on bike, tyres, bones, arse etc)
Portsmth - Sant route (18/09 - 30/09)
£505 Bike + Ferry + 1Pax reserved seat (rtn)
£100 sustenance (rtn)
Total £605 (4 berth cabin is £135 each way, so an extra £70 rtn with 4 of you sharing) = £675.
The above prices are today. If you book when they open their "Black Friday" window in Nov/Dec you can bring that down by about £100+.
£100 - £150 each way (worst case and being a good sheep). Is it worth it?
, nice empty roads to razz about on two or four wheels, cheap coffee & plonk…. Can’t think of any other benefits that would suit me though 
