Did not find a topic to post suggestions for cheap transducer solutions. But here we go… Options are wider with NMEA 2000 than 0183. But alternatives do exist:
Garmin intelliducer: 170-230 USD on Amazon.com. Two versions: Transom mount, Thruhull mount. The thruhull mount can be acquired in nmea 0183 and 2000, transom mount is 2000 only. Note: Verions for two different hull angles also exist.
This smart transducer has been implemented before by ardupilot enthusiasts (using Arduino and radio comm). Solution is simpler than mine, pinout available here:
Also available in NMEA 0183 and 2000. Adapts to hull angles up to 22 degrees. 7 degrees beam width. Min debth 0.5m. 1 data update rate per sec. The Airmar P39 transom mount has similar specs, but a wider a wider beam of 15 degrees. P79 measures depth only, the P39 also temp and speed.
Available with various cables (like for Garmin) and in various prices (150-300 USD) on Amazon and elsewhere (typically around 240 USD)