That is seriously expensive coffee. FWIW I think a short story ought to be priced in proportion, so if a three hundred page book cost say five whatevers, a fifteen page short story by the same author would be worth five per cent of that, plus a little bit for the admin involved in selling it. So .25 whatevers sounds about right to me.
Of course, if i have never heard of the author and there aren't any reviews going, I might decide to wait and see if a short story comes up free, or a full sized book not free, but with a worthwhile sample size available. After all, it isn't as if I'm short of something to read.
I take your point about the work, but buying a book by an unknown author is a bit like saying to say, a decorater "choose what colour you paint the walls, and how well you do the job, and I will pay you up front whether I like the result or not."
So, sorry, but the first book I buy from an indie has to be cheap or I just won't be buying it.