I spent almost as much as that for a 2 Powerwalls and installation in 2019. (Granted, I got a 3rd back from various incentives that probably weren't available for DIY.)

DIY (like this project) is only "worth it" if the person doing it enjoys the work or values the lessons.

There is a spectrum of DIY and the sweet spot depends on the person. Since I'm good with electronics my sweet spot is buying premade packs.