We got the same type of quote for our kitchen. There is a $10K difference between custom and semi-custom. This was for an apples to apples comparison: same hinges, same thickness of plywood in bases, same number of drawers, same drawer slides. I think we'll go with the semi-custom. Stock cabinets come in sizes that are multiples of 3", 9", 12", 15"...60", etc. When your kitchen has an inch or two space, they have matching spacers that fill in those spaces and look like extensions on the cabinets. The factor I'm concerned about it the color of the stain. Most semi/custom stock will stain certain colors with or without glazes. If you want a certain stain color, they may not be as flexible as your custom cabinet guy. Another factor in durability is how long the shelf run is and how thick it is. Without good support, a long run will sag in the short term; a thinner shelf sags sooner. I will probably order a door from each before I make my decision. I ordered one door awhile back; when it got here, I realized the cherry wood the cabinet company was using wasn't top quality. A great installer with an eye for detail is what makes ordinary cabinets shine. My son just had a bottom of the line series installed. We had them put plywood in the bottom of the sink base instead of particle board. They look high end because they go to the ceiling, there is a nice crown molding up there, and he doesn't have low end knobs. They are just a builder grade cabinet with a dark stain over birch. They won't last as long, but he doesn't need them to. My builder cabinets I have now are 20yo and are just starting to show their wear. The funny thing is that my sister who is married to a contractor and have built their own houses with custom cabinets thought I had a custom job. No, I just had an installer who takes pride in his work, cabinets that went up to the ceiling, and plywood panels installed on unfinished sides. I guess my conclusion is that I'd go with the customized in-stock cabinets and save the $$$.

I'm certain those in the Boston area (beantown?) can recommend a good local custom cabinet maker. These can be competitive in price to any mid to high end manufacturer. I went with Crystal, which is made in Minnesota. In the price spectrum, it is considered mid-high. I am quite satisfied thus far, as I near completion.

I work a lot with Woodharbor cabinets, and one nice thing is that you can order your legs and other moldings from White River or Enkebol and Woodharbor will finish them to match any of their cabinet finishes including any color paint. It's only about 50.00 to finish a leg or stick of crown and you get a beautiful factory finish that's guaranteed for life. It also keeps you from paying the high markup cabinet companies put on items they have to buy somewhere else, because you are in essence buying it direct from the manufacturer. I'm sure there are other companies that do it, but Woodharbor is the only one I've worked with so far. You can't beat it in my opinion.

If you are near an Amish cabinetry maker, you may find they can do the kitchen for the same cost I have Crystal Cabinet Works beaded inset cabinets and I'm very pleased. I purchased mine during a "free paint" and "free inset" promotion. They allow you to combine their Keyline (less customization, lower price) and full custom offerings that keeps their pricing in the mid to mid-high category. (They were far less than the Fieldstone). They have a good reputation here and among my preferred contractors. There is a good thread here on pricing comparison of white painted shaker cabinets.