Trail Boss is so bulky that it comes in 9 ounce containers because that's all that will fit in a standard "16 ounce" powder container, however, the price pretty much reflects the fact that you are only getting 9 ounces and not 16 ounces.
It's kind of handy because if you have your Dillon 550 set up to load .357 magnums with the powder measure calibrated to throw a magnum load of slow burning magnum powder, you can essentially leave the powder setting alone and use TB for a cowboy action or plinking load instead of resetting the powder measure to throw a correct charge of W231, Tite Group, or Clays.
I also like the fact that if you try to throw a double charge, the case will overflow and you will know something is wrong.