Hey Whopper, the Humminbird Helix 7 with Sonar and GPS would be a great unit in that price range. For a mapping card you could use either the Navionics + or the Lakemaster chips. I use that exact unit with a Lakemaster Great Lakes chip for Erie / Detroit river and its a great combo. If you wanna keep it closer to $500 with a mapping chip, the Helix 5 Sonar/GPS would be a better option. I have a couple of friends that have recently bought the Lowrance Hook 5 with Nav + card and they seem to be happy with their choice as well. Raymarine Dragonfly units are another good option to look at too. Hope that helps.

Patrick