I too am a big DIY'er....
But you need to compare apples to apples... in this case it is not fair to compare a the price of a Jackalopee (with stuff like diagnostic LED's, strain reliefs, connectors, proven track record, etc) to a no frills design (which I like...it does the same functions, but doesn't include any extras). Your pricing doesn't factor in connectors, heat shrink tubing, extra wire. I am sure that the first edition Jackalopee built for his own use was built for $50 or less but has evolved to a pretty much plug and play device...hence the price difference.
Not bashing you, I would probably build my own as well.
A fairer comparison is to the Hoppy 46255, which can be had for $60ish.....same basic functions but no frills as compared to a Jackalopee.