Most of the difference is in quality of parts used. Mainly the hook, skirt thickness, and paint. You also have where it is manufactured. Most major store bought brand jigs are imported. Almost all of the custom guys like myself or Northstar are made here in the USA by guys that like to fish. I started out making jigs because I became frustrated with the subpar products coming off the shelf.
Custom isn't always more expensive. If you look at my Big O jig at 3.50 each which is .50-1.50 less then many store premium brands. Honestly it is a better jig with better components.
I do make jigs with a rattle band and sell rattles as an accessory. I'll even install them if you ask.