So, these two things add up to "custom made control board"(?)
adding emphasis
2) Control board for any machine.

as stated: "As a small company you have two chances a) custom made at a custom price".
Nothing Arif brought up involved "custom price" he merely listed "me too"s.

Making a "PLC" (I have yet to see anyone here making a PLC, many claim to make one, but none are PLCs in the meaning understood by the industry).

What I am pointing out, as I have, unfortunately, seen it too often, is that making a thingy and selling it to someone is not the end of the story. If someone buy a "Control board for any machine" for $75 they STILL want full support (and that can take you more time than it took you to design the thingy) and, if the thingy requires YOU (as most small run thingies do) to take care of every step of the use, you WILL lose your shirt, if you have sold it as a "standard solution". If, however, as you, Jan, suggest with other words, that you approach someone re custom made at a custom price, yo can include the cost of support in the price.
If, however, you go out and 'compete' on the PLC market, you better be prepared for some huge costs AFTER you have made and sold the thigies. A full fledged industry standard PLC can cost $1000 and be manufactured (in the volume e.g. AB run with) for maybe $75. Do you REALLY think the $925 is pure profit? No, most of it is "support costs"

Erik