A lot of simple living and personal finance advocates say you should drop expensive hobbies and take up cheap ones. This makes sense, but there's also a place for "frugalifying" hobbies that are typically expensive.
When I went to college I met Linux enthusiasts and became interested in Unix system administration and networking. To pursue those interests I needed multiple computers. I was a working college student, so buying several new computers was out of the question.
I poked around and learned three important facts: 1) computer equipment depreciates very quickly, 2) it's possible to tear down and reassemble a computer using with only a screwdriver and patience, and 3) free Unixes were available (Linux and BSD) and had very low system requirements. So I started scrounging around for free or cheap broken, derelict computers, pulled them apart, and built computers that met my needs from the parts.
This became a game: when I needed more hardware to try some new setup or run some new service, I would try to cobble it together from spare parts I had on hand. If this wasn't possible, I'd try to find some free or cheap parts that would be sufficient. I ended up with some weird solutions sometimes, but it was a fun creative challenge and I learned a lot.
The point of all this is that I found a way to participate in a hobby I enjoyed in a frugal way. Most of my computer geek friends pursued the hobby by running "gaming PCs" or by being Apple diehards. Those paths involve buying brand new hardware all the time, which gets very expensive (not to mention wasteful). I'm glad that I didn't give up due to sticker shock, since the hobby has given me a lot of enjoyment, and also bolstered my resume and helped open up some career options.
So it's possible to pursue conventionally-expensive interests in frugal ways, if you're willing to turn things on their head a little bit.
My other main hobby is cars...I've really got my work cut out for me there. More on that later.