A couple of cheap effective things I have been using:
Breathing exercises. Buteyko Breathing has been the most helpful. “Slow Breathing” and Coherent breathing are also helpful.
Through your breathing, you can take control of your nervous system. You can google all of the above techniques
Meditation: Meditate twice per day. Start with Concentration Meditation techniques, and them progress to mindfulness meditation, such as body scan meditation.
Earthing: The EMF we are exposed to creates a lot of stress. Earthing reduces stress hormones (cortisol) during the night and has many other benefits are well. You can buy an earthing strap for sleeping for about $30.
The above are all very cheap and very effective at calming the nervous system.