When I had a machine in for servicing and waiting for a part, I was loaned a 1600P.
Discovered very fast that it IS a work horse, and would jump at it if I had the chance (and need).
A very simple, plain-jane machine, but one that is highly sought after by those doing lots of stitching.
Price ... to me, $600 sounds like a good/fair price.
Though the only way you would know if it is, is to find out what the going prices are in your area.
Keep in mind that by no means is it a new model.
The big questions for you to ask yourself ... is it going to do what you want it to do?
What does it not have that you need/want?
What extras do you get with it?