Sometimes, you need to remove the cartridge to then try to determine what brand and model it is. With the large quantity of brands and trims available, it's hard to be able to recognize who made the guts without seeing them.
There are generally three types of shower valves:
- single handle
- two handles: volume and mixed temp
- two handles: volume and thermostatic control
Most of the thermostatically controlled ones literally have marks or sometimes numbers on them to give you an indication of the temperature. The other two types will each have an internal limit stop that limits the amount of hot water you can mix in. A thermostatically controlled valve will have a calibration adjustment internally so that it will match the markings on the outside. From your picture, I do not see the normal markings I'd expect on a thermostatically controlled valve. In the list above, the cost of a cartridge generally goes up as you go down the list. The two-handle job in the middle should not cost $400, but the bottom one could, depending on the brand and model. Also note, some brands have a life-time warranty on the cartridge, so if you can identify it, they may send a cartridge for free, but they are also very willing to let you buy a new one, too!