The seagate 100 gb drive is 200.00 from Best Buy or 176.00 from newegg.com.
Installing it in a 12 isn't impossible if you are comfortable doing such a thing.
The screws are tiny. Just go slow and be careful not to rip any ribbon cables.
I did this last week with no problems. Typing on my 12" 1.33 w/ 100 gig Seagate right now.
Heat is the same, power seems to be the same too.