Seizing a perfect opportunity for shameless self-promotion, PolarCOM is a comprehensive set of NMEA instruments. It acts as a standalone repeater/set of dials and is commonly used to get 2nd (and 3rd and 4th) set of instruments elsewhere, including commercial vessels where it provides convenient data in engine rooms and elsewhere down below. It is very much in your price range (free
We also have a complete navigation product to do everything else - i.e. vessel on the chart, routes, waypoints and other usual chartplotter fare.
AIS is not available in current version but is under development now and will be available in the next release (by Q2 2010).
All that, as usual, at Polar Navy
And, to be fair and also because someone else will come up and say it anyway in a minute - google OpenCPN