Custom costs double. By custom I mean custom sized, hand made. The non custom, made by machine or made in china, always come in 3 inch increments and cost about half.
Not that non-custom sellers wont bend and give you a cabinet or two in a custum width, but in general lines it's all 3 inch increments.
Another way you know they are not custom is they will have fillers on the ends or in between cabinets like trim moldings on the faces.
Ultimately the choice of custom over mass produced , with the available quality lines in mass produced, is really a personal preference. If you mind fillers or even the less conspicuous trim fillers pay double for hand made to fit your kitchen exactly if your budget can afford it. Otherwise just buy the made in china ones and be happy that you got them for so cheap.
Of coarse you could always just shrink your kitchen to fit non custom kitchen exactly with no fillers and you could create the impression that it is a custom kitchen to the less discerning eye.
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