Sure. Some of us burn spare fat, some get by on a can of baked beans, others go to a Michelin starred restaurant for their dinner. Which amount will you judge as appropriate to pricing this up correctly?
Well that depends on the person. Just because something is difficult to measure it doesn't mean it doesn't exist.
I would suggest the best way for me would be to add all my food costs, attribute a fifth of them to cyling and divide by miles travelled. Then I can live on caviar or baked beans and it would give a good enough approximation of costs for additional food.
I've been reluctant to add up what cycling costs, mainly because I don't think I would like what I found. I'm pretty far down the food chain as far as fancy kit is concerned, but it still costs a fair bit. Put it this way, I get 12p a mile at work for using my bike and don't think it comes close!