Saint-Just itself is tiny — a handful of stone buildings, a parish church, and farmland — so the commune is best treated as a base for slow countryside days, not a checklist town. Almost every budget-friendly anchor (walks, the Vieux Chemin, Norman farms) is free, which is why lodging and food rhythm drive most of your cost.
Real savings come from what you do around the village: ride a TER to Rouen, walk the Vernon market, or cycle to Giverny instead of booking a paid Paris day tour. Plan around May or September, when lodgings in Vernon drop 20–30% versus July–August and the light is still good for the hedgerow country.