There is lodging of all kinds and for all kinds of budgets in Deventer:
A nice campground in an old park just on the other side of the IJssel River (easy walking or biking distance to the old center): Camping de Worp
Hotels, B & B’s, etc. (This is the webpage of our local tourist information office with nearly all the lodgings in the area. It is in Dutch, but you can get an idea of what is available and for what price.)
Participants have been happy with Adamshof and Het Papenhofje.