I've been looking at various options the last few weeks.
I already have a bulkhead compass, and NEED some type of depth finder, and would LIKE to have a better GPS charting solution.
The lakes here are either extremely large and shallow (with sand/mud bottoms), or medium sized, with rock bottoms with depths varying from over 100ft to 2 feet, in very short distances.
There is a reason that aluminum fishing boats are the most common thing on the water here.
Many of the lakes are not mapped at all. Locals know the way, and if you are lucky there are jugs floating to mark either hazards or channels (you need to guess a bit)
Keep in mind... in Canada, chart data is not free. The cost of digital charts is goofy.
Depth:
I picked up a barely used, Lowrance Mark 4 GPS/Depth unit for $76 USD.
Besides GPS, it has NMEA output so I can run it into a DSC radio or something else.
While I likely won't use it's charting functions, the extra GPS data source on board may come in handy.
The GPS function will also allow depth logging, for making my own charts. (Insight Genesis or other similar projects)
GPS/Charting:
I still like paper charts... I like them for their size and simplicity. They don't need batteries either.
As a second info source, I have been using a old handheld Garmin GPSmap60cx, which I use when chartering.
I have been using a 10" netbook for "beach bar passage planning" and data transfer to the Garmin.
I've been thinking for a long time, that combining the planning and gps functions, into a portable device would be nice, so I have a 10" waterproof android tablet inbound. So far I plan on using Boating HD and OpenCPN on it. Portable, multfunction (AIS, weather, communication, movies...) and the charts are MUCH cheaper than a "normal" chart plotter and the rip off prices they charge.
EDIT: here's hoping the transom mount transducer will work inside the hull. The New Design C22 has no coring in the bottom so it "should" work.