After working with Riley, my assigned customer service representative at PCBWay, I've reduced the number of assembled boards in my order from 5 to 1. This saves quite a bit off the bill; the tag is now $62. That seems like a steep price for a Feather-sized PCB, but given that it's a single prototype (and I still get 4 boards without the parts), that's not too bad. I can let out a more formal run, with a lower cost per assembled board, once I'm sure it works correctly.
Between my own finances and delays at PCBWay because of the coronavirus outbreak, I'm waiting until at least 5 March to actually pay for and order the board.
(As a side note, while I'm not clear on whether Riley is male or female, this individual is really incredibly helpful and dedicated to doing a good job. That's something I've noted with Chinese companies in general, and I've been told is simply a part of Chinese culture. Many of my fellow Americans could learn a thing or three from them in this regard. I'm not always happy with the product itself, but customer service is top-notch.)