You can easily do it for free, or nearly so. You don't really need most of the stuff affluent folks like us buy.

A second-hand junker, or the local bike mission reduces or eliminates the initial cost. One of the local bike missions is in the church behind my building. None of the guys it serves are concerned with lights, bells, cleats and pedals, panniers and racks, or cycling outerwear. No toolsets or flat repair stuff either. They just ride. When it breaks or flats, take it on the bus back to the bike mission and get it fixed for free. Who needs panniers to carry your returnable bottles? They hold nothing compared to a plastic trash bag anyway. And across the parking lot, the church ladies have lots of clothing they give away.

Finally, they don't turn you away from either place if you happen to have a job or a home. I could just as easily use their services rather than online shopping or the LBS.

So bike commuting doesn't have to cost anything. It's a CHOICE that folks like us make.

That said, I cycle like an affluent person. I own four bikes--one is titanium and two others have full fenders and racks. I've spent a small fortune in lights (both battery and dynamo hub), clothing, pedals and cleats and all the usual accoutrements talked about here.

But, because I don't even own a car, I can afford to work part-time since I don't have to support a car. And the bus is even cheaper. (Here an unlimited ride pass on the bus is $56/mo, or $672 a year. I own wheelsets worth more than that. Several of them.)

I ride a bike because I like it. I deeply enjoy it. It's the best two parts of my day. Screw all the rest of the reasons usually bandied about. ThermonicScott said in a recent thread, "I ride to work just because I enjoy it, but I keep getting told it’s for other reasons." That sums it up for me.

So why not just get honest with your wife. It makes you happy. Isn't that alone worth it all? (And if she isn't concerned with your happiness, that's a whole different thread.)