It can be as cheap as you want it to be. I think my bike is pretty nice, though objectively only an entry-level road bike. I improve it from time to time so it's not like I'm a fanatic about spending nothing but I save thousands per year by biking to work. I would never trade the time spent commuting for a half hour in my easy chair so it's a no-brainer. Save thousands, enjoy yourself more, indulge in a cheap hobby. And that's just the selfish (albeit honest) reasons.