I'm about to buy a 6" independent 4-jaw lathe chuck. ENCO has their
free shipping promo on this month, so I was looking there.

They have a no-name with threaded mount for $99.95 (ENCO #271-6382):
http://www.use-enco.com/pdfs/157.PDF

or

Bison plain back for $156.95 (ENCO #240-3064):
http://www.use-enco.com/pdfs/160.PDF
& it's "semi-finished" threaded back plate for $43.95 (BTW it says this
back plate is for self-centering scroll chucks, do you think it'll work
with the independent jaws chuck? There's no finished back plate shown
explicitly for the independent jaws chucks.)

I do believe that you get what you pay for, but I also believe in buying
what I _need_, even if it's not always the "best". So, what does the
$200 Bison have or do that the $100 no-name doesn't? With an
independent 4-jaw, all you really need is that the jaws are parallel to
the spindle axis, right? How much worse will the no-name be than the
Bison in this regard?

I expect that the chuck will get very little use, so durability is not
something I need.

If I get the Bison, how fussy would I have to be in finishing the
semi-finished back plate? My lathe experience was in high school shop,
45 years ago.

I hope that this doesn't provoke a debate or too many rants about
Chinese crap. My apologies in advance if it does ;-)
Bob