you can get a dellorto carb w/o parting out a bike. but what is a carb worth? well, it always depends on how much you're willing to spend.
i think most moped shops sell a dellorto (complete) for around $50 (or more). but for a carb that's been used, i'd say no more than $25.
i can't really tell from your post, but i think you want the dellorto for a motobecane? it should work ... but i've heard there are a few problems making the conversion. the dellorto is really for italian mopeds (if it's a 12.12, 12.9, 14.14, or larger). if it's a 12.9 or 12.12, its' for a vespa and probably no good for anything else. however ... some dellortos were made for bikes that have separate choke cables ... i have no idea how those work or whatnot on non-italian bikes (which don't use that kidn of carb).
i don't know what tool box covers you are referring to, so i can't anwer that question. just go by what you're willing to spend, i guess.
finally, you have to be a bit more patient for answers. it might take more than a few hrs for someone to give an answer to your specific question.