When you make an option agreement, or a purchase agreement, the buyer must give consideration which is basically a tangible form of payment. You could be the most amazing negotiator in the world and manage to get someone to option the rights to you for free. This however is not legally binding. There must be an exchange of tangible payment in order for this agreement to be hold up in court. Payment could be anything. It could be one dollar, or a shoe, or a tissue; it just has to be tangible. Usually, if the rights-owner is willing to give up the rights for free, the consideration is one dollar.