Ice Fish,
I work for Navionics and if I can answer any questions from anyone on this site let me know. lcarr at navionics dot come. In reply to your question, it depends on a couple of factors:
1) What plotter are you going to use?
2) Where are you fishing?
3) What size kind/size boat?
4) What is your budget?
ANswer those questions and we'll go from there.
I will also be at the Toronto Show this weekend...stop by if any of you are at the show.
Larry