Calculations for buying used products

Circling back to my Day 2 post: our purchase of a used bike and how to calculate that into the equation.
Chris Jones, Staff Research Associate for Renewable and Appropriate Energy Laboratory at University of California, Berkeley responded to my inquiry. Here is what he had to say:

On buying used goods I believe it is reasonable to assume that emissions are related to price of good. If you buy a bike new, use it for a while and then sell it for 25% of the original price, then I believe it is reasonable for the first owner to assume 75% of the manufacturing emissions, and the new owner to assume 25%.

Manufacturing generally produces about 500g CO2 per dollar spent by consumers. So an average consumer product with a cost of $1000 produces about one half a ton of CO2. Producing a motor vehicle requires about 10 tons of CO2.  I haven't seen studies on LCA of a bike, but it is likely under half a ton of CO2.

In our calculator bicycles are under "entertainment" goods. You could try putting in different prices (on a monthly basis) to see what you come up with...actually, I just did this and I come up with about 0.2 metric tons for a $500 bicycle or 0.4 tons for a $1000 bike, or $400 grams CO2 per dollar. If you spent $100 on the bike, then that would 0.04 metric tons.

So what do you know, here I was thinking I was saving CO2 but in the marketplace it appears I'm just assuming 25% of the manufacturing emissions.  I'm still thinking about processing this as a net gain of zero because we perhaps saved this bike from abandonment in a landfill.