The reason I'm suspicious is that I got my current gauge set from a friend
who gave me his least expensive unit while disparaging gauge sets that
only cost a hundred. He said he paid about $200 for the one he gave me.
His "good" one was $350. (Then again, that was a few years back.)

Found the adapters at a NAPA today for about $25; they wanted about $70
for a Robinair hose set. They sell a complete brass manifold with hoses
for $99. A Carquest quoted me nearly $100 for three hoses alone; the
drone behind the counter was incredulous when I started walking away,
even though I had just said I could buy a whole gauge set for that.
Advance has an Interdynamics hose set for $40; I might settle for
these if I can't find better.