It's important to still have fun when you are on a tight budget - it helps to maintain your mental health.
Look for parks and nature trails that are free to use where you can take peaceful walks and enjoy your surroundings. The exercise itself will help you to feel better too.
Consider volunteering. Helping out at an animal rescue centre, for example, would be a great help to that organisation and would also be an enjoyable experience for you - walking a waggie-tailed dog who will soon consider you to be the highlight of his day, or petting an old tabby cat that has been starved of attention since her owner died.
And for something more relaxing, there are many free TV channels available through Freeview or you could read a book from your local library.