Wayne, where are you located?

Wayne, it's difficult to give generic answers in terms of which equipment you should buy based on what you have but there are some factors that can influence you in one direction or another. One of those would be the brand of the electronics already on the boat. For example, if the boat has an older but working Raymarine autopilot on board your integration options are a little better sticking with Raymarine equipment now, the same can be said for matching older fish finders with replacements from the same brand. But, most 15 year old equipment is old enough it's not going to matter too much. 15 year old radar units are very unlikely to work with current equipment, etc. 

Cost of the units can be found pretty readily and I frequently find Hodges Marine a useful place to go comparison shop prices. I also strongly recommend getting your hands on all the brands of equipment and figuring out what works best for you. Just because your friend swears by one brand doesn't mean that's all you should consider.  All four brands (Furuno, Garmin, Raymarine, and Simrad) make extremely capable products that will safely aid your navigation wherever you want to go. 

Lastly, Furuno has produced a really good series that compares the user interface of all four brands' current products. They've put stickers over the other brands but it's very easy to tell that System A is Garmin, System B is Simrad and System C is Raymarine. 

-Ben S.

Thank you, Ben, very helpful.   It currently has this original equipment:  Raymarine ST60 Tri-Data; depth, speed & distance log, Raymarine ST6001 autopilot w/dual controls.  Upper helm has a Garmin GPSMAP 702/902.  No radar.   

With that in mind, any further recommendations or suggestions?  TIA.