If you don't want to go industrial - think about finding a class 15 Japanese clone zig zag machine and a generic walking foot. It isn't the perfect solution, but with careful handling a Japanese zig zag machine will do what you want to do, since you are not doing production work. You can leave it set up and ready to go and if you burn out the motor - oh well - they made millions of them, buy another one.
Good ones to look for, and this isn't a complete list, only what I can think of at 5:30 am
Morse Fotomatic
White: post 1950 to pre 1970
Wizard
Fleetwood
These brands usually use regular short shank feet. With Kenmore and some other more familiar brands you may need specific feet.