If there really is a motherboard issue, that B150 board is a decent option.
I can only recommend getting a second hand PC for parts harvesting. Look for something with an i7, swap the CPUs, and maybe the memory if what they used is better, re-sell the PC with the smaller chip for half of what you paid. CPU upgrade for $50-100. Or you can keep the secondary computer, donate it, etc.
Something like this:
i7-6700, 16GB memory, 1TB hard drive, $129. This would be for component harvesting, not a board swap.
https://www.newegg.com/dell-optiple...e-office/p/1VK-0001-6EN38?Item=9SIAH59JJV8021
The ones with non-proprietary motherboard form factors are more expensive generally, and starting with 6th and 7th gen it isn't uncommon for even the Micro Tower systems to use proprietary shapes for the front I/O. (Some will fit in standard ATX and Micro ATX cases, pay close attention to the motherboard mounting holes. As long as that front I/O doesn't stick out too far, they are usable)
Most of the Dell also use a proprietary power connector. Adapters do exist though.
https://www.moddiy.com/products/PSU...Adapter-Cable-for-Dell-OptiPlex-Inspiron.html
Not really seeing any HP Microtower out there for reasonable prices. The second hand 'gaming' PC market scoops up all the decent ones and sells them with a cheap GPU, and some RGB fans added.