Radar vrs. GPS & radar
I bought the Raymarine SL72RC+ radar/chartplotter last year and am quite pleased. The cost was about $2K with the GPS sensor (I''ve forgotten the model number). You can use as a radar, a chartplotter, or split the screen and see both radar and chart images at the same time (great for figuring out what''s a buoy and what''s another boat in the fog. The color units are about $1K more, and I didn''t feel it was worth it, although I must admit the legibility is probably the worst part of the unit I have (b&w). I think the color units allow you to superimpose the chart on the radar image in a different color.
The Raymarine unit will always operate as just a chartplotter, you can even disconnect the radome and use it that way. The radar does switch off and on independently.
I guess what you sacrifice is the ability to see both radar and chart images at the same time, full screen. But, I''m not sure you''ll be able to have both displays cover the exact same area unless you go with two Raymarine units (HSB, more $). Perhaps Furuno or someone else offers. The real advantage of an integrated radar and chartplotter is having the range and orientation of both be exactly the same so you can easily match up what you see on the radar with what''s on the chart.