I decided that once I get this project working well, that I might make several for family and friends that might need something like this. To that end I placed an order for some HC-SR04 (Ultrasonic Ranging Module) and the HC-SR501 (PIR Sensor) modules from a company in China. They're dirt cheap compared to what you can get them for in the US. Adafruit is selling the PIR sensor for $9.95 vs. the 87 cents I paid in China (and you know they are getting them from the same place!). Radio Shack sells the Ultrasonic sensor for $29.95 vs. the 89 cents I paid in China. I bought 20 units a piece (which gave me a price break from 92 and 90 cents, respectively - and free shipping!). I've bought quite a bit of stuff from China through a web site called AliExpress, which looks like an online mall for the Far East, and have had no problems with any of the vendors. Granted, depending on the shipping method, delivery may take a while. I also got the LED strips and LED strip mounting rails from this site. Other stuff I got in the past were Arduino Mega 2560 for around $15 a pop and various forms of NeoPixels (strips of various densities and individual ones mounted on heat sinks - plan to use those for wearables or crafts), so I've had some successful dealing there.
Both sensors are from the same vendor.