Your 2000 Z3 is all OBD2 so is easy to diagnose. Like wise the 116i.
Maybe you should look at setting up your own diagnostic kit. There are cheap and expensive options, depending on what you want to do:
INPA software (free) on a windows laptop with the cheap special USB cable and an OBD2 to 20 pin lead for the Z3. Reads all modules and lets you code new modules to your car. Software and some instructions are here: https://www.bimmerforums.com/forum/showthread.php?2184573-The-Z3-Diagnostics-Thread-Instructions-Experiences-Discussions-Experimentation
Creator C310+ scanner. Low cost, reads all modules. Will not code new modules.
Foxwell NT530 with BMW software. Mid price. Reads all modules but will not code new modules.