I have an older model gpsmap 76s; at that time, they were about $300! If you want charts, you can load it with Garmin's mapsource BlueChart Americas. It shows all of the structures and depth contours you would expect. Here's an example of a map near the Coronado Bridge (SD Bay):
Back in the day before gps/ff combo units were available, you could hook the 76 up to some of the Humminbird Matrix FF's. I don't know if they still have that compatibility, but you may want to find one of those Humminbird cables. It will enable you to run your gps off of the FF battery. Leave a couple of AA batteries in the unit for backup in case your main battery dies.
I've been caught a few times on the water when the fog rolled in. That's when it is really nice having GPS! But do yourself a favor and get a backup compass, just in case your GPS dies. REI has a nice one for $10.00 (Brunton 9030). Just leave it in your seat pocket or pfd. You'll probably never need it, but if you do, you'll be glad you had it!
