Soleil Plage is a lovely site, I agree, but is expensive, and books up quickly. Right next door is La Bouysse, which has the same access to the Dordogne, at a lovely spot on the river, a good pool, etc., and is a lot cheaper. The advantage of these sites, over some others, is that they are tucked away on a back road, away from a lot of the traffic in that area. You can do canoeing from the site - they have their own canoes at the river bank. There's a nice 'fairy-tale' castle within walking distance through the woods - the Chateau du Montfort, which can also be seen from the river.
However, there are lots of absolutely first class sites in the Dordogne area - and I'm sure you'd be happy on almost any of them.