This is a little controversial. Singer 600 and 603 Touch & Sews. Make sure you read the instructions. Other than the wind in place bobbins they are very similar mechanically to the 400 and 500 series Singers and are all metal inside. Later models have plastic gears.
You may want to bring a screwdriver with you and ask to open any machine you're interested in to check inside.
There are a lot of good Japanese machines out there but you would have to check on an individual basis.
Rodney