What is an 1198 hd worth these days?
No such model as a 1198 HD. There is only the 1198c SI Combo.
$500-$800 should be the price range depending on condition. Add a couple more $100 for the 1199ci HD SI Combo value--newer model with a faster processor.
Humminbird Helix 12 CHIRP SI, 1198c SI, 1198c SI, ONIX 10 SI NT, Helix 7 CHIRP SI GPS G2, 360, RC-1