I purchased my JBJ ATO so I could sleep better at night. The guy at my LFS
was trying to save me from buying the $120 piece by telling me how to build my own ATO. It involved splicing extension cords and "jimmy-rigging" pumps and floats for about $40. I'm not a fan of messing with electrical wires more intense than speaker wire (due to some past bad experiences).
If you have confidence in your own electrical work, want to save money, and can follow directions on YouTube and other threads on here, then DIY. Otherwise, spend the extra $80 and sleep soundly, like I do.