Re: Recreational boater - marine GPS
Unfortunately I think that question is a bit complex. It is nice to have a Chart Plotter, but if you also want a fishfinder, you either need the space for two units, or buy a combo. You quickly turn this into a $500+ proposition.
The cheapest solution is a monochrome fishfinder (or depthfinder) and a handheld charterplotter.
BTW - The GPSMap units (430, 530) are designed for inlake lakes, and are very easy to use. They are a bit pricy.