I'd think an ETA quartz version would be under $150, or somewhere arounfd there. That would make a nice beater and a very good value. If they can do a 21J for 108, they ought to be able to do an ETA quartz and get a premium, because their is an authentic quartz version. I'm not so sure I am ready to POP 600 on a used beater quartz watch. I would, however, drop $150 on a quartz rep in a nano second. I think others would too. IMHO, it would be one of their top sellers.
Being a Quartz rep it would be very low risk for first time buyers.