Get it on appro, rig it up at home and see what it can see by way of lampposts and tulips bushes etc in the garden or somewhere else safe like open space, it should run off your car battery successfully.
If like many of us you only get caught out in poor vis twice a year, it should be fine.
If it does not work, I guess the parts may prove difficult to source now.
I have a Furuno 1623 which cost me €500 secondhand, but works as new.Guess do not pay anything for this until you know it still functions.