Not all firearms are purchased.
Not all firearms are new.
Some things come in trades.
Others show up in pieces and need some love.
Some come as part of a group of firearms.
And, once in a while, someone gives away their "garbage".
It is still quite possible, in today's world, to 'horse trade' your way into something for a minimal investment. (Or, in the case of the $28 derringer, to horse trade my way out of a bunch of crap that came with it, to reduce the investment.)
Always thinking about MSRP or retail pricing on a firearm is a sure-fire way to always price yourself out of the market.
And, in this case, the question wasn't whether or not it's worth buying a derringer for BUG duty or deep concealment; rather, the question was does anyone use one.
For me, the answer is yes:
When, for whatever reason, I feel that even the LCP is too big to carry, the little .22 LR derringer comes out to play.