Does anyone know where I can get this set (all 4 seasons, 81 episodes) cheap? I have looked and the cheapest I can find it like 50$. Please help me. Thank you

Where is a legit place to buy it from. I have found some places where it is like 37 dollars but those seem to be copied DVDs, which I don't want. So I think I can get it for like 53.99. What is a legit site to buy it from?