🚀 go-pugleaf

Practical Peripherals has a 2400 MNP.  You can get them, in the SF Bay
area, at Frys (Sunnyvale or Milpitas).  Around $230, I think?

MNP does a great job of filtering noisy lines:  If someone else in the
house picks up the extension and shouts into it, I don't see a single char
of garbage!  And it supposedly speeds up batch transfers (I don't know
from personal experience).  For interactive stuff, it's slower, and
introduces an annoying lag.  So, personally, I'd recommend not using
it unless you have noisy lines.

PP also has a cheap, reliable 2400 baud.  I've used their modems at home
and at work for a few years now with no problems.
ComputerWare (Palo Alto, Sunnyvale) advertises something like Avatex for
$166.  I've seen ads for something with a "z" in it for $139.  Not MNP,
these last two.