Here is a really cool piece of technology that is both affortable and very very cool.
https://www.youtube.com/watch?v=rFyYNBBCIFcI have this installed on my boat and it works as advertised. It is very very easy to use. All you need is the vex sonar phone and the navionics app.
It will create or update charts for any body of water even if it is not listed on a map. As soon as you record it and upload the logs (which it does automatically when you connect your device to a wifi signal) navionics will process the logs and create the charts from your logs. Its incredible.
Scott