I am in the same boat as you, my build is easily starting to turn into a money pit, and it gets quite frustrating at times.
Feel free to laugh at some of my mistakes:
-No, a weldless kettle wall mountable RTD probe will NOT screw into an NPT sight gauge Tee, better find a SS plug online! Don't forget the o-ring!
-No, that home depot load center is NOT large enough to fit your PID, outlet, e-stop and terminal blocks (figured that one out after cutting various shapes in it)
-Oops, did you forget to include a 1" inch SS shim washer in your McMaster-Carr order? Well home depot doesn't sell those! Enjoy more online shopping shipping charges!
-Sorry, you don't own any step bits, bi-metal hole saw, bi-metal jig saw blades, knockouts, and other assorted hardware - But you will once you realize you need them!
-Last, but certainly not least, working with 10ga wire is a tremendous pain in the b@lls
A few weeks ago I was feeling like a horse's patoot for not just saving up and buying one of Highgravitybrews systems pre-built, but when it is all said and done, I will have a system that is built exactly to how I want it, is expandable to add another vessel later on, and will hopefully allow me to brew faster, and with more control.
Plus, I imagine it will be a kind of pride thing, knowing that I build the whole thing myself. I'll let you know if I ever get there.