Question on Lowrance HDI Chirp to HDS

Hey everyone,

I would like to buy a Lowrance HDS 7 Gen 3. I currently have a Lowrance Hook 7 and Lowrance HDI Chirp. Both come with the HDI Transducer. I was wondering what I would need to get the HDS unit fully installed on my boat and how much the going rate is currently for a Lowrance HDI Chirp 7inch model or the Hook 7 model. I'm kind of weighing my odds if it's worth selling one of my current units and upgrading to an HDS model if it won't cost me a whole lot more after the sell of one of my current units.

Thanks for the help!

Also to add to the equation, I have US2 capabilities built into my ipilot trolling motor. I do not know if
That will save me money or not by not needing a structure scan Transducer.