There is a bewildering variety of routes and means of transport for getting to France and we have tried most of them. St Julien is about 500 miles from Calais/Dunkerque and about 350 from Caen. Realistic journey times are around 8 to 9 hours hours from Calais and 6 hours from Caen. I can supply routes that seem to work, including how to get round Paris avoiding the dreaded Boulevard Périphérique and a route from Calais via Rouen (the route we normally use).
There is intense competition, particularly on Dover/Calais. Eurotunnel, DFDS (ex Norfolk Line) and P&O are all based in Dover / Folkestone and cross to Dunkerque or Calais. Further west you can cross from Newhaven, Portsmouth, Weymouth, Poole and Plymouth to ports such as Dieppe, Le Havre, Caen, Cherbourg, St Malo and Roscoff. Try Brittany Ferries, Condor Ferries or LD Lines.
There are also comparison sites such as directferries or ferryon line.
Whichever way you go, it is a long way and you may consider an overnight stop. There are several chains of cheap hotels.
You can also fly with Ryanair, City Jet or Flybe from Stansted, Gatwick, Newcastle, Edinburgh, Glasgow, Dundee, Inverness, Leeds, Liverpool, Manchester, Birmingham, Southampton, Bristol, East Midlands, and Exeter to Poitiers, Limoges, Brive or Bergerac (all about 1.5 to 2 hours from the house). Or take the train to Angoulême in about 6 hours from London. There is a bus from Angoulême to Brantôme that meets an evening train from Paris 4 days a week. Car hire is easy at airports and Angoulême station.
You can even arrive by bike - several people have! I took 6 days from Caen, but others have done it more quickly.