For a project I've been working on I have been using the extremely cheap and easy hc-sr04 ultrasonic sensor. Now I'm looking to downsize without making my budget go up. I bought some of these from Adafruit but the barrel of the sensor sticks out of the board too much, and they're 20x the cost of the hc-sr04s I bought.
What I need is an ultrasonic sensor for cheap (<$20 usd) in a really small package, that can operate at 5v or less, and is Arduino compatible. It sounds like a lot, but any suggestions would be greatly appreciated. Thanks!