Doable on the cheap in a mobo with a outboard via the French canal system to the Med. Pick your time carefully for the channel crossing and you might want to buddy up with somebody.
You can find something around 20 - 24 feet pretty cheap by watching ebay and prowling the cheaper canal marinas. 5 to 10£k should get you something that would do, less if you get one that needs TLC. I might be tempted to get a 4 st Honda outboard either new or nearly new though. £3k
On a sailboat across the channel, round Brittany, across Biscay and down the Atlantic coast of Spain now that will be much more expensive and could be some real hairy chested sailing.