I use a Hummingbird Fishin' Buddy 120. They run about $160. The Fishin' Buddy is not the most hi-tech, but all you need is the depth, lake bottom contour, and possible fish detection. They are really portable and completely easy to set up. I try not to depend on it for just finding fish, but wouldn't be without it when trying to find depth changes within a lake.

Loufly