Download the original text from Project Gutenberg (legal and free). Then, find a “Vocabulario de La Celestina” (a vocabulary list) online. By reading the original with a pop-up dictionary (like Chrome extensions), you create your own Nivel 1 experience. Is it harder? Yes. But it is free and 100% legal.
If you specifically need the simplified "Nivel 1" student version for a class, you do not necessarily have to buy it: la celestina vicens vives pdf gratis nivel 1 better
If you cannot pay, do not pirate. Instead, use the public domain original combined with free adaptation tools. You will learn more, respect the literature, and actually finish reading one of Spain’s greatest tragedies. Download the original text from Project Gutenberg (legal