I just found it
http://guides.macrumors.com/Buyer's_Guide
I like how it has the time cycle and when you click on the older release dates it will show you the price and features.
The problem with that site (and others like it) is that there is no way to accurately predict when things are due for updates. All those sites do is show you when things were updated in the past. There is no discernable "timetable" for the update process, and that is proven by the dates they list for a product cycle. The dates are sporadic at best, thereby rendering that site (and others like it) useless.
There is no "average lifespan", rigid cycle, or any regularity to the updates that occur.
These sites simply speculate, which is no more than you or I could do.
:black:
If you are looking for anything even remotely close to a guide as to when you should buy an Apple product, then you have two events to focus on... the WWDC and the MacWorld Expo. If you are looking to buy a system more than 3 weeks prior to one of those events, then simply buy it. Forget about waiting.
If you are looking to purchase something and one of those events is less than 3 weeks away, then waiting may be beneficial, but by no means a guarantee that anything will be changed or updated to a particular product line from Apple.