I agree with that post in that DIY options can often be more fiddly and more expensive. My first E-bike experience was exactly that. I thought I'd save a bit by purchasing a $50 900w currie scooter motor and building an ebike around that. I soon discovered there were multiple challenges involved that I hadn't accounted for... fitting a sprocket to the opposite side of the rear wheel, or doing a jackshaft, or driving bike cassette with a front-freewheel. I wound up spending more money doing the latter, but I was really proud of what I had put together, and it was fun to ride and be able to shift, and it out-performed many of the kits available at the time. Top speed of 35mph back in 2008-09! I did all this without the Endless-sphere resource, and learned a lot along the way. One more reason to get into DIY versions is like john61ct says below, because you enjoy it. I'd add the 4th reason: educating yourself and adding to your skill-set.
John I couldn't agree more! I'd have just bought a Radwagon if I really wanted a cargo bike without any of the fuss of building it. I mean that's only $1500, and I've already spent ~$500 on this build... and a BUNCH of my time.
I'd re-frame the argument over a make-vs-buy decision away from "saving or spending money" to "what do you want to spend, time or money?". You're going to spend both, you just have to decide how much of each is worth it to you.
I'm game for designing a DIY battery pack that someone can print and get components for on amazon/ebay. I'll put that project in a different build thread though, right now I'm exploring different design ideas.