We can begin a list like the air we breathe, scenes of beauty that we see, the gift of our Savior or the land we live in. Upon closer examination it becomes clear that it is a wonderful life, but you can't live for nothing. We need to pay taxes for services, we need to buy food to eat so that we are healthy, and travel can be costly. No doubt the greatest "free" gift ever given to mankind is the freedom Jesus Christ has given us (Galatians 5:1).
The free gift of grace through Christ is there for the taking—but only if we pay the cost. We need to believe in this gift, repent of our sins, be baptized and then live in a way that is pleasing to God. That was the direction given by Peter when he was asked what could be done (Acts 2:37-39). Everything has a cost and we are left to judge whether the price being asked is worth the cost we must pay. Eternal life certainly is worth all.