Flex circuits are not that hightech nor expensive. IIRC the per square inch price of single layer kapton flex PCB is comparable to your traditional four layer FR4 board.
On the other hand large amount of cheap(-ish, as it tends to include even high-end AV receivers) tries very hard to avoid FR4 and multilayer boards in general (apparently in high enough volume making four times larger board than required and the huge setup cost for THT assembly autamation makes economic sende)
On the other hand large amount of cheap(-ish, as it tends to include even high-end AV receivers) tries very hard to avoid FR4 and multilayer boards in general (apparently in high enough volume making four times larger board than required and the huge setup cost for THT assembly autamation makes economic sende)