If those WERE my choices ($500 vs. $2800) I'd go with the new furnace. But
the big question is:

$500 for a new motor sound rather high. $2800 for a new furnace sounds
rather low. What exactly are you getting?

First, buy one for $60 and install it yourself. Or call
local hvac to install one. Don't forget to change run cap.
( Also it is a good idea to discharge existing cap prior to swap )

As for $2800 for bryant 310 no thanks, this is builder model
( worth about $600 ) I would ask for 312 only few $ more, or even
better go with 90%s.

Don't listen to idiots who claim they only install "own" motors,
even if they do, plenty of others that will.