Okay, the cost of the battery will be cheap - you'll probably spend between $20-$25 through http://www.macsales.com
. As for the hard Drives, good luck - if you find one, they'll probably cost as much as a new iPod Nano. (I found 80 and 120 GB, but not 100 GB, in spite of Toshiba's site boasting of one.) The price of the hard drive alone is where you'll eat your costs at.
I also noted, while on Toshiba's website, that they have a 240Gb PATA - wonder if it might be compatible with the pre-video iPods.
that'd be a mod worth doing, since Apple has yet to break any ipod beyond the 160GB factor.