Dakṣiṇa (दक्षिण) refers to the “offering of a gift”.
Dakshina is usually offered after a spiritual teacher, practitioner, or holy person has made an offering to you. These offerings are usually in the realm of energy and spirit and therefore cannot be physically measured. This makes evaluating their worth impossible and it can make knowing how much to donate a difficult thing to decide.
In Hindu Society, Dakṣiṇa is considered a necessary part of completing the spiritual practice. When we give Dakṣiṇa after receiving spiritual teachings, a retreat, a course, or a ceremony it is considered a way to finalize the practice and invest in our spiritual journey. If we receive without giving back there is an energetic imbalance, it is understood that Dakṣiṇa is an energetic exchange that brings balance and cultivates the proper space for us to fully receive all of the teachings/ceremonies, etc. Spiritual scriptures tell us that we must be willing to make sacrifices in order to authentically pursue a spiritual life. We make emotional sacrifices by offering our prayers and in ceremony and sacrifice of the mind through meditation and focus but we also must make physical sacrifices through the offering of money or goods. Money is often seen as a dirty thing in the world of spirituality when in actuality money and spiritual study are coming from the same source. The simple energetic exchange of money and teachings brings balance and harmony. Your donation is also not being made to one person or teacher. It is being made as an investment not only in your spiritual journey but in the spiritual journey of those around you. Thus the money that you offer is fully utilized so that all can receive the fruit of these gifts. So how do we decide how much to donate? There is no amount that can be too small or too great. Any exchange is the right exchange. However, it should feel to some degree like a bit of a sacrifice. Maybe it is a sacrifice of the cost of your morning coffee, or extra groceries, or a part of your savings. A sacrifice should, however, not feel pain or put you at a disadvantage. Sacrifice comes from two parts sacra (sacred things) and facere (to do or perform). To make a sacrifice is to perform a sacred act and sacrifice implies "doing without something" or "giving something up". So the question is not really what were these teachings worth? But what are you willing to do without in order to receive the full benefits of the teachings which are, in themselves, invaluable.