I think that if you are in the market for a machine to sew through layers of thick fabric, I would look for a used industrial machine. You can come by them at flea markets, Ebay, and sometimes even garage sales. If you don't plan to make that many bags, I would suggest getting an old sewing machine like a Viking, Bernina, and even an old Singer. These machines have metal gears and if the foot piece can lift high enough and you use a leather or Denim needle (preferably a leather one) then you have a chance sew through lots of thickness. My old Viking could do this easily. The only problem was that the foot wouldn't lift high enough when you had to sew through a double seam.
However, I would not, under any circumstances use a Featherweight machine. Yes, they are true workhorses, but if you burn out the motor, you are looking at least $200 to buy a new Chinese motor to replace it.