A local real estate agent is probably the best way to go, but, if you don't mind putting in a couple of hours yourself, you can use
REALTOR.ca - Welcome to try and find similar properties.
I see some vacant lots on the north end of Bob's, but there doesn't seem to be much listed for the southern portion of the lake.
Of course, land values can vary by a wide margin depending on location, access, shore type, terrain, etc.
Why not just contact one of the "big name" realtors in the area and asking them for a preliminary appraisal? You should be able to get a rough idea of a reasonable asking price without committing to a listing.