This is one we went through recently.
With new RIB on order we decide to go to the Southampton boat show to get the "other bits" I had decided on Raymarine 7" mono units after many weeks looking throuh catalogs and on the phone. However as Denise (my wife) had the job of navigator I said have a look round and see what you like and find easy to use.
We spent many hours looking round the stands and in the end bought almost nothing I had set out to buy.
Be vary cauious buying without using. We thought the 7" raymarine radar cahrt plotter would be hard to use. In short try before you buy. Also there was hugh differences in speed of redraw etc, to the level that I think of one that if zoomed in close would not keep up with a powerboat/RIB running fast.
In the end we ended up with a Garmin 10" 2010 and twice the price but that was what Denise was happy with, and have held of on radar for the present.
It does come down to cost but even between mono and mono there was hugh differences between the clarity of different screens. The same was true of the colour screens and them daylight brightness is an issue. As far as Charles comment about Raymarine being the only daylight viewable ones. I disagree here the new Garmins are very good, never seen the two side by side but have never had a problem reading the screen even when very bright sunlight has been direct on the screen. But agree that this is onething to be careful about.
Also the menues of some was very long winded and hard to use.
I think boat shows are idea places to try and see things, some that looks the dogs "bits" is catalogs we was not impressed with at all.
Have a look and pick what suits you. I would now not consider a mono chart plotter after using a colour one, but ther are many that use mono ones with great effect.
But as a personal preference, colour chart plotter always, and as big as possible.
Colour radar but smaller screens are OK and the overlay feature and MARPA is good. However be careful to use the overlay feature on radar you need lits of extra bits at quite a higfh cost, if you dont what this feature go for mono radar.
Fishfinder would always go mono as we dont use it for fishing.
One other think to ask is warranty. We was told by some if you fitted the equipment yourself it must be inspected by one of their agents before they would honour the warranty, one one company quoted over £300 foir this
And on one last thing shop round we got our package for over £300 less than " and were not making anything at that price" quote after a bit of quote beating between shops
Hope this helps