I also am curious on the price break down from home depot! Seems really HIGH to me! Im guessing HD is adding a percentage on top of the flat fixed rate they probably pay their sub contractors. And, they also probably give a high estimate because they dont know exactly everything that is needed for each install, such as wire, breakers, conduit, permits, PoCo fees, etc. BECAUSE they havent had someone check out your house and service panel!
Your best bet is to buy the generator yourself and get quotes from several local electricians who have done generator installs and go from there! Most of the contractors working for the big box stores are hacks and cut corners because theyve agreed to do the work for a flat rate/set price, SITE UNSEEN! Qualty could be compromised!
And dont forget, u may need trenching for electrical and plumbing, a plumber to do the plumbing, and someone to pour the concrete pad! Thats 3 contractors right there if u cant do any of the work yourself! Another thing to consider is whether your gas service(if natural gas) is large enough to support a generator. Not to mention that the gas lines in your house may not be big enough to support a generator, which then u would need to run a gas line back to your meter!
A LOT more goes into a generator install than just the electrical....