sonar/mapping gps question

[whitetailfrazier]

i am looking to upgrade my electronics to something with a mapping gps splitscreen.  i have looked on ebay and some other sites, but i am having a hard time figuring out which ones i can get the topo feature on.  alot of them say mapping gps, but it is just an outline of the lake.  i want one that i can get the chip for and it will show me depths, and contours of the bottom. can anyone recommend a few of these in the lower price range that are decent.  i am willing to buy used, and willing to do some shopping just need to know where to start,thanks.

[Mike Cork]

If you can find someone willing to part with it the Lowrance 520c is the best unit I have every owned. Unfortunately they quit making it and went with the new HD models, jury still out on these so far so good.