...Reading, of course!
I love to read. I simply cannot imagine a life without books. To me, words can take you anywhere, make you feel anything. And happily, reading is the simplest, most frugal of pastimes. I don't need special equipment, I don't need to go to a special location, I don't need anyone else to join me, I can combine it with other tasks (having a bath, on the bus, waiting for an appointment).
I use my local library a lot. It's not a large library, but its very friendly. I often take out books that I wouldn't consider buying, books that I am not sure I will like, because it costs me nothing to try them, and sometimes I am pleasantly surprised. My library will order books free of charge, and I've never had any difficulty getting hold of something I want to read, even if I've had to wait a week or two.
I do like to buy books, too. I enjoy having a good old root around in charity shops, and most of the books I buy come from there. I keep an eye out for authors I like, and that my husband enjoys. In fact, I keep a little list in my purse of all the Iain Rankin novels he owns, so that if I see one I can quickly check if he already has it. I rarely pay more than a pound per book in a charity shop, often a lot less.
Even if I end up paying full price for a book, I consider it good value for money. For about the price of a cinema ticket I get several hours of entertainment, even if I only read it once (and I often re-read books that I have enjoyed).