doesnt that new little bird have it all -- SI DI Gps along with 2d all for less than your 500 budget plus able to use lakemaster chips.
HUMMINBIRD HELIX 5 SI GPS
Brilliant 800H x 480V, 5 in. 256 color display with backlight
Sonar standard Side Imaging/Down Imaging/DualBeam PLUS
Precision...