Explanation
-더군요 reports something you found out or observed in the past with a note of surprise or realisation, combining the retrospective -더- with -군요. Attach it straight to the stem (비싸다 → 비싸더군요, 있다 → 있더군요). It is close to -더라고요 but a little more formal and reflective, so it suits telling a story to someone you are polite with; the plain form is -더군 or -더구나. 그 식당은 생각보다 비싸더군요 — That restaurant turned out to be pricier than I thought.