the DSI model I saw on their website was $499. The lowrance dsi does NOT have 2d sonar, only DSI, and the picture is not anything like a 2d sonar pic. Fish show up as little white specks/dots in DSI, not arches or fish symbols. The non DSI Mark 5 is $200 or less, and will show fish symbols or arches depending on the settings.
The Down scan image shows structure in much more detail than a 2d sonar picture will but any fish usually show up as little white specks or dots from the pictures I've seen and some reading done. Look thru the electronics forums for down scan threads, and you can probably see some down scan pics posted, or google down scan pictures.
GO BIG ORANGE !
I meant to behave, but there were just way too many other options available at the time.