I recently wrote a tutorial on making a small brass hammer, like the ones shown in the pictures. You can access the tutorial here.
You can make a hammer like these for less than $10. Glen Drake sells some like this for quite a bit more.
Chester toolworks sells some very nice plane hammers, also (just to put in a plug)
Mike
[You can get the 7/8" brass from Online Metals. If you want a different size head, look here.]