Does this generator quote make sense?

All - I am helping a relative who is in the process of purchasing a Kohler generator. Just for some background, this person owns a 2,200 sq. ft house (on a slab + 2 car garage) in the Deep South (think AL, GA, NC, SC etc) and is looking for a generator that can essentially allow them to operate at “business as usual” capacity in the event of an outage, brownout, etc. (Essentially, they want to be able to run a normal set of electrical equipment – furnace, AC, refrigerator, etc. along with lights with some power left to spare; just to add, they have upstairs/downstairs AC/heating units). My relative got an estimate from a local dealer rep – which I’m including below.
1) Is it conventional to calculate the power needs of the AC / furnace together - are they really additive like this quote suggests?
I’m not an expert – by any means – but right off the bat, it strikes me as somewhat aggressive in terms of calculating power needs (not to mention a calculation error in determining the power needs for the lower power generator).
2) Also, both of these models retail for significantly less than what this quote suggests - what factors would drive those costs up to those levels?
Any help would be greatly appreciated. More than happy to answer any follow-ups.
Thanks much.

The 30RESA (125 amps) will be enough to power both upstairs and downstairs AC/Furnace.
Your furnaces combined = 30 amps
Your AC combined = 45 amps
That’s a total of 75 amps.
Leaving us with 50 amps for additional appliances.
The 30RESA is able to do up to 125 amps. Some appliances will have to be added to that, such as your refrigerator so you don’t lose food, but not to exceed 125 amps.
The 20RESA (75 amps) will be enough to power 1 AC and 1 Furnace Your furnace (up or downstairs) = 15 amps Your AC (up or downstairs) = 25 amps That is a total of 50 amps Leaving us with 25 amps for additional appliances. I feel with this generator you will only be left with your freezer and very few lights.
We will add grounding rods on every system we install
The maintenance for both systems will be the same cost. It will need to be serviced twice a year.
The price for the 30RESA is approx $19,000 The price for the 20RESA is approx $13,000

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I see the error but also maybe they are going for worst case scenario in their math.

I don't know what those units retail for but I am assuming this company is including installation and whatever else will be needed to have a working system?

As a follow-up ---

The 30RESA retails for ~10k.
The 20RESA retails for ~4k.

Given that I'm not an expert, what "installations/add-ons" could be driving the cost? In the case of the 20RESA - 9k to install a generator seems excessive. This generator will be installed on a flat area of the yard next to the house, so it's not like there is a retaining wall that needs to be built to accommodate it.

Am I missing something here? Thanks again for any follow ups.

You are missing all the electrical work that will need to be done to tie it into the panel and any gas work if they are power by natural gas.

In addition to the labor/installation costs, the contractor has to eat too, so they markup the price of the generator.
I question the calculations on the A/C units. They typically run 30amps each.