your "seems on the low side to me" from the original post
told all of us that you have little or no collected experience
with accordion variations and pricing, and may be basing your
feeling on aBay/Craigslist ASKING prices rather than selling prices
readng back some threads on student level accordions would help
basically accordions have sort of harmonica looking things inside them,
beginner accordions have one or two, student accordions have 2 or 3,
(the number of shifts and names on them are often misleading on student instruments)
higher level student/semi pro instruments have 3 or 4 internal "harmonicas"
and usually of higher quality components (reeds mostly.. a lot of them..)
and a better "feel" due to higher quality action/bellows
so a standard 2 reedset student (first level step up accordion) from a beginner model
as was built and marketed in the 50's and 60's during the heyday of accordion schools
is still a dime a dozen and not often built well enough to really last but some can
still be found that are decent and playable a very, very few are actually nice..
their only/actual value is to you personally as there is no quantifiable re-sale market demand
as all accordion sellers generally have more beginners accordions in the warehouse
than they will ever be able to find buyers for, there being almost no children students
to be found, and adults who come to the Accordion generally realise and quickly look for
an intermediate model, of which there are also still many to be found, and which
are vastly more worth playing as they have better feel, better sound, more possibilities
good luck, be patient, expand your craigslist search to the maximum distance you
would be willing to drive to pick one up, or just go to San Francisco some weekend
for fun and visit an accordion shop or two along the way
find a nearby accordion club if you can and attend a meeting or two