Nanci, Your trip sounds great. The virtual collapse of the dollar has caused all of us travelers some heartburn, but we now consider it just another challenge. Your problem with one-way car rentals has often caused us grief. Like you, we normally turn to AutoEurope or Kemwel (a sister company) for help, but its seems like they have almost made in impossible to do inter-country one-way rentals without paying huge drop fees. At times, we have actually taken a train or bus to the nearest city in another country just to rent a car. But, for Toulouse this does not work well since you would probably have to go all the way to Perpignon to get a car in France, and by than you are halfway to your destination. Since you are going up to Deauville, you could stop at Honfleur for lunch and have some of their great moules while looking at the harbor (we love Honfleur). As to Cinque Terre, its really a neat place. We once tried to hike the 5 towns, but it was too darn hot and my wife had not yet fully recovered from some minor surgery. So, we had to turn back. One of these days we will try this hike again when we have a few days in the region.
We wish you the best of luck finding a reasonbly priced rental car. Barcelona has an excellent local tourist office and they would be a good source of help. At least you know that there is a bus if all your efforts fail. Hope you love the cruise.