Even though they've been discontinued by Lowrance, they're still out there ... but, the best prices I've seen are on eBay. Something like $300 tyd for a new one and around $190 (current bid) for a used one. Have not seen one advertised for sale in the Personal Classifieds of this site, so I have no idea what price a member owner would ask. It is possible that some member has one and would sell it ... but, you'd have to put a WTB (want to buy) post in the personal classifieds forum and wait to see if someone replies.
If you don't need GPS & still want a 5" screen and Down Imaging .. check out the Lowrance Mark 5X DSI unit (but, understand that it's a greyscale unit ... not color). And if you want a 5" screen, no GPS, and just a 2d broadband unit (83/200kHz) then look at the Mark 5X Pro unit. Lowrance retails these two units at under $200 ... so you should be able to find them for less by searching for them by model description (mark 5x pro or mark 5x dsi).
... cp