As I learn from reading articles (Timezone.com and others) the use of a movement can mean many things and varies per company and model of watch. What I enter here is based on reading and not on actually taking apart watches and observing (as some fora folks are capable of doing).

It may still be called a Valjoux 7750 if, say, a bridge is used as the basis of the otherwise completely in-house movement (not sure if it counts if a watchmaker adapts a manufactured hairspring, but it might--the Swiss are very strict and protective about designations and honors). Or a manufacturer may use the whole ebauche and kaboodle. According to text IWC redesigns and remakes the entire movement, but it is based on the manufactured original.

Chronographs are complicated watches--many parts and jewels. The problem with taking an existing basic movement and then adding to it or changing it in order to create a chronograph (or should it be called "chronoscope" as I am learning--since the watch does not scribe anything) is that the movement was not designed for that sort of loading (either extra or eccentric) and will not perform well over the long term. Hence a high quality manufacturer will redo the whole thing.

Why use an existing movement at all if it is going to be completely redesigned? As our distinguished Rolex Texan suggests there are some machines that are classics and worthy of a long run or emulation, such as the Ford 289/302. It is so good that it is worth taking apart and tweaking (even with completely new and forged, cast, machined parts) to modify it for the specific task (racing for 24 hours or for a few seconds). That may be comparable to what some watchmakers do to base movements (chronograph? dual time? annual calendar? display back?).

In many cases the higher price reflects relative real costs. Hopefully someone with more knowledge can rate these watches.

Did your try Thomas Mau's AP group yet? Nice folks and willing to share/help.