I do alot of flat packs for customers.
If you use a cabinetmaker you will get the following,
Custom sized cabinets
Better quality board
Blum hinges
Bigger choices of materials and colours.
Much better quality overall.
It should cost that much more either if you buy it flat pack.
Agree 100% here. Just ordered a whole heap of cabinets panels etc to expand my current kitchen from one of the custom on-line joinery companies who happen to be a local joinery/kitchen business. Price wise it has turned out cheaper than Bunnings etc and I know the fittings, runners they use are top quality, Hettich in their case and the product (talking cascaras) are made locally not in China.
On top of that as I was expanding my current kitchen I needed 'non standard' sized base units to match and to fit into a fixed space I have some odd sized cabinets, for example 1 is 556mm wide. Then add in replacement doors for my existing cabinets with the mounts drilled exactly where I want them, and made to my exact sizes. Certainly couldn't have done that with an off the shelf flat pack unless I replaced the whole lot.
The only real gotach is you need to know what you are doing because what you order is exactly what you get, though guess if you go to someone like CuttingEdgeKitchens they will more than likely provide some value add to get it right at little extra cost. In fact the company I used have a design service for around an extra $70.
So yep the message is there don't discount a local joinery or on-line business. Not everything at bunnings/Ikea etc is cheaper and rarely is it better, but yep it is convenient.