Thanks, this makes the picture more clear.
    They are not advising systemic antibiotics, but intrasulcular
antibiotics.  IOW, they plan to put an antibiotic substance in the
sulcus between the tooth and gum.
    There is a place for this, but according to periodontists I know and
trust who have used these agents, they should be used SELECTIVELY.
    By that I mean that their patients get an initial workup, oral hygiene
instruction, scaling and polishing, perhaps scaling and root planing as
needed.  The mouth is then re-evaluated for healing.  Some areas may
require other treatment, such as surgery.  Some areas may be borderline,
and SELECTIVE  use of these agents MAY get enough improvement to
eliminate the need for surgery in questionable areas.
    Billing it this way may mean a number of things, but IMO these agents
should not be used indiscriminately.  Your dentist may wish to avoid
surgery; still, the need for these agents should only IMO be determined
AFTER scaling and root planing.
    In other words, I share your opinion that they are trying to bump up
the complexity and expense of your treatment plan.
    There is a chance that they're just making a pretty treatment plan to
show an insurance company (and you), but obviously they expect no
benefit from the insurance company.
    I would get a second opinion.

Steve

The fees for the scaling & root planing, as well as the fillings, seem
rather low -- they are definitely below average.

Is that because the insurance plan sets a cheap rate? That would depend
on the type of insurance plan you have. Some are reasonable, and some
set unreasonably low fees.

When the fees set by the insurance plan are too low to cover the dental
offfice's basic expenses like rent and utilities, then it only takes
simple arithmetic to figure out that the dental office cannot survive
by performing services for less than their cost.

That may be the case here: I don't know, but the fees seem to point in
that direction.

When the fees are too low, it has been common for the dental office to
make up for the deficiency by selling you something else. It doesn't
take long to apply the antibiotics, and the revenue is an additional
$540, which should be more than adequate to cover the true costs of
your treatment plan.

My question is: if you suspect that the dental office or the hygienist
is trying to sell you something you don't need, in order to make up for
the unrealistically low fees listed on your treatment plan, then:

1. How do you know any of this treament is needed in the first place?
2. If it is needed, would you trust that it would be done WELL by the
people in this dental office? Why?

Perhaps you do need all the listed treament: I don't know from the
Internet. Perhaps you should start by choosing a dentist with a good
reputation and NOT trusting some insurance-plan marketers to do your
choosing for you. You would be medically well-served by paying an
honest fee to an honest dentist for honest treatment, and not messing
around with the insurance shenanigans -- which are just as much the
fault of the insurance companies as of any dentists who try to twist
these plans into a reasonable fee.

Best regards,
- dentaldoc