Ah, so you mean how to estimate, for example, EC2 on-demand instances. Sorry I gave you lots of info you didn't need!
I have read those price matrices and I admit to being totally clueless as to what an "instance" is. If someone loads up a page that leaves them connected as a seat on your database, and they type a word into a formfield, and they go on vacation for 3 weeks, is that an "instance"? (Rhetorical question, I no longer have room for this sorta stuff in my head and just hire the gals & guys who take care of that part of a job)
kazar