I actually don't save that much my biking because I try to keep all of my expenses cheap.

I have a 1995 Audi A4 w/60k miles that I bought for 3k€. It gets used about once per month for a round trip to the extended family (about 500 miles) ... which costs about 130€. The maintenance is minimal and insurance/registration runs about 1000€ year.

The bicycle was 799€ and throw in a helmet and lock and it's around 900€. I run my old clothes when I ride it.

The subway is subsidized by my work and I get a full city pass (including airport) for 26€/mo.

I guess all my expenses are low (except for my 2000 USD/mo student loan payments.)