Croissant

That varies considerably based on the price of your ingredients, the size of your batch and how big you're making each croissant. Even the recipe that you use could cause the average cost to vary.

This also varies dramatically by what your time is worth to you.

However, baring this, here's what my average batch costs me:

Flour. approximatly one pound. $1 (I buy my flour by the 50 pound sack)
Butter. two sticks. $1.50 (I wait until the nice cultured butter goes on sale, buy a bunch, and freeze it)
Sugar/Milk/other ingrediants.  Nearly inconsequential, but I'll round up to $0.50

So then if I don't count my time, a batch of croissants costs me $2 in materials.  I normally get 10 croissants out of a batch, so that comes out to 20 cents per croissant.

Again this comes down to time though, croissants for me are an all day process.  I'm stuck at home all day, and only will make them for a special occasion.  If I have a hankering for a croissant, I'll go to the local (good) bakery and spend the $2-4 for one.