Vendée is a touristical place, and there is a large choice of accomodation, especially at the seashore.

Here are some ideas around Sainte-Gemme-la-Plaine:

Campsite:
A Campsite ground is available directly in the wedding place. A bathroom and a kitchen will be available.

Hotels:
Hôtel Le Bordeaux in Luçon
Web site

B&B and vacation Houses:
Airbnb
Abritel