Take a peek at https://www.ebay.com/sch/industry4.0-ppd/m.html
Cheap stuff from a new seller! Only 16 feedback ratings but all 100%. Either a scam, mistake, or a new seller moving parts at cost to build up a reputation. All guaranteed through Ebay either way, so if you want to take a risk like I did, stock up! Between prototyping and teaching, I'm burning through parts these days like never before... and thus hoarding more than ever!
74 cents ($1 Canadian) for ultrasonic sensors, 40pc male/male jumpers, FTDI adapters, much more.