I cycle to commute to work.
I got my trek for free via my work which had a rewards program back in 2006. I rode the hell out of this mountain bike and over the years have replaced the chains, chain rings, derailleurs, cables and of course tires and tubes. The only part which I thought was expensive was when trek sold me a tune up for 150 dollars and my bike did not feel any 'tighter' or when I had to replace a wheel after 10 years. Over the last 12 years I probably spent about 500 dollars total for my hobby. A very very good trade for how much i love to ride.
This year I took my tax money and purchased a real road bike for 1095.00. I also got a new helmet 85.00, new glasses for cycling $85.00, new pedals (45.00) and a new back pack for commuting (110.00). All of these items were very huge upgrades to what i had prior to this February. I am very very happy to have spent this for my commute and my hobby.
I also build computers as a hobby, now that is expensive and has risks involved in possible hard ware failure... i think cycling is the better deal.