Don't know about Garnmin maps but I LOVE my Humminbird 787c2! In the under $500 range BassPro has the Humminbird 383c with split screen and built in GPS antenna (nothing to mount/drill holes for!!!) with the built in base map for $399, and the 595c at $499, both are color units. They are comming out with new units and models, if you can find a 787c2 on sale you might get it for $500, the detail is amazing compared to my prior Matrix units and light years ahead of my old 200dx!!
Humminbird says "Compatible with seamless Navionics Gold & HotMaps cartography on MMC format"