It doesn’t sound like you have pricing for both nor have you seen the products of both. That is truly the only way to judge. You aren’t comparing anything, neither price nor quality. In addition, my custom cabinetmaker installed his cabinets. He made certain everything was plumb, level, operational-perfect. My previous house had semi-custom cabinets for a simple kitchen and my designers’ installer was also a perfectionist. In our first house, I would have been thrilled to have the cheapest cabinets from a big box store. It really is a matter of what is it worth to you and what quality level is acceptable to you. Not every custom cabinetmaker is a craftsman, nor is every ore-fab well made.

I would not consider drawers to be "custom", they are what most consider a better way to store and organize things in a kitchen. Fillers are used to make sure that cabinets/drawers fit and function well in a space.