I think that's a great idea, but I'm not quite sure how one would implement this idea. I wouldn't be comfortable requiring people to enter that information. (Some may consider it proprietary, and then there's the matter of asking people to supply more information when they upload . . . the more that's asked, the greater the deterrent to upload.) It also already takes a ton of moderator time (mostly mine) to make sure that photos are properly catalogued.
I think your best bet may be just to ask . . . If you see a cookie that you're particularly interested in learning how long it took (or cost) to make, feel free to ask the creator in the comments area under the cookie. I think this would be a terrific dialogue to start to foster. But I think it needs to be generated from you all . . . as opposed to something that's mandated by me or the site.
I have found that everyone here has been most generous with input when asked!