Home Depot - the exception.What is the rule?

[StillHope]

Aloha,everyone.
As Rob mentioned a while ago (and I checked recently) Home Depot on the mainland(at least in CA) has the same price as in Hilo.
This is the exception of the general (+ shipping) prices.
What is the rule of thumb to determine the approximate price(NOT on FOOD )?
Is it like 30-40% more?

Note: I am asking for the practical reasons,not to start the general discussion.

I talked to the sales rep.in Home Depot,he recommends to buy the fridge in Hawaii(warranty,etc.)

I also will need a dining table and some other furniture items.
Garage sale is not good in this case,because I like everything in one style.
So
1)-are there are other stores like Home Depot
and
2)-what is the average % over the mainland price?

I would appreciate your input and patience)):
Thank you in advance.