I do find it interesting that the two things that have helped me most aside from therapy, namely mindfulness practice and Nonviolent Communication, are both largely about mentalization. Thich Nhat Hanh, who has been my main teacher about mindfulness, suggests a lot of exercises like saying "Breathing in, I am aware that I am (angry, sad, happy, whatever). Breathing out, I smile to my (anger, sadness, whatever)." That is mentalizing in its essence.

Nonviolent Communication brings in other people. In NVC, you might say something like "are you angry because you are needing more respect?" Again, awareness of mental states.

Those things are not expensive to learn. You can find books on NVC or mindfulness at your library, and videos on youtube also. Going on a full-time mindfulness retreat costs as little as $50/day. Good adjuncts to therapy in my opinion!