I would "Haunt" eBay for a week or so and see what is going for what. I upgraded that way to second generation (Blue Connector Network -- LowranceNet) Lowrance GPS Chart Plotter (GlobalMap 6500) which is radar upgradedable/compatible, and a Lowrance X-107C DF Sonar. I have not installed yet, but I also picked up a Lowrance LMF 400 guage with a fluid level sensor and a fuel flow sensor. I would caution regarding the differences between second generation lowrance networking blue cables and third generation lowrance networking red cables. The "Cross Over" cables from one generation to the other are very hard to find. Stay with one generation (Red -- Latest & Greatest). My next planned addition to the network is going to be a New Lowrance VHF radio to replace my old one. The Lowrance VHF Radio is "Networkable", i.e., tied into the GPS, so coordinates are automatically transmitted when broadcasting an emergency or man overboard.

You do take some risks with the eBay stuff but the prices you can get stuff for are NICE and well within your budget. Also (!!!!!) Color Rocks, don't know how I could've live so long without it. I would make that a mandatory requirement.