What's the absolute cheapest unit I can get to collect data for creating a contour depth map in RM, and how much is it?
I don't care about any bells & whistles (screen size, color or b/w, etc.).
I don't care about seeing fish or objects.
I don't intend to load maps back onto the unit at all.
I don't want/need side-scan - just depth measurements.
Will be collecting in <70ft of fresh water.
I would like to collect the best quality depth data, which I believe requires 200KHz down sonar capability, correct?
Would prefer sdcard data collection, but internal memory would be OK as well, with retrieval via USB (assuming it has enough memory for roughly an entire day's collection)
Old/used units are fine, as long as I can find them on ebay.
Edit: I'm thinking the Lowrance Mark-4 might be a candidate?
Thanks for any recommendations.