One reason HP ink cartridges are so expensive is that the heads are an integral part of the cartridge, as you mentioned.
My first ink printer was a EPSON which had fixed heads. Over time, those heads got to the point where they needed to be reworked. I got several quotes for the job ... could buy a new printer for near the same price. So, I bought an HP. Pay more for the cartridges, but I get new print heads each time.