Recommendation for Depth finder replacement?

I am looking to add another depth finder/sounder to my boat. Anyone know the cheapest option or the best place to get it through? I am looking for the basic round gauge with the thru hull transducer. The depth finder in my boat now works okay in deeper water. Say over 10ft deep. But once you get under that it says like .2ft or some bogus number like that. I would like to add another for assurance. I have played with the controls a little trying to get it to work but it doesn’t have any options to change. It is the factory lowrance depth finder that came on my 99 X-Star.