Here's a comparison of Tour magazine tested mass data for medium-to-large frames taken from three articles:
- steel bikes, Aug 2013, on-line summary
- "sub-800 gram" carbon bikes, Dec 2013, on-line summary
- titanium bikes, Sept 2014, purchased today in print version
This sample is biased in favor of the carbon since the carbon frames selected are the lightest, most expensive available, while in steel, for example, a custom builder like Rob English, emphasizing weight, can get lower than most stock steel frames, which have less emphasis on weight. But I think the Crema represents this quite well: only 1512 g for the frame.
Forks are heavier on the steel and Ti bikes, in general, but I am focusing on frames, since forks can be selected, especially with custom steel, which is still a lot cheaper than those carbon bikes.
Result: best carbon is 704, best Ti is 1350, and best steel is 1512. So the cost of Ti is around 646 grams, and the cost of steel around 808 grams, relative to carbon.
808 grams: that's not bad at all. Still within typical daily body mass fluctuations.