I just received a crapload of Opera records (some as early as the 1930's), how do I go about finding out their value?

I have enough to fill up the trunk of my car. :)

My g/f’s Uncle just sold his 1920’s home in Detroit. The house is gorgeous and was filled with antique. Both her Uncle and his former lover (now deceased) were antique dealers. The former lover was an opera fanatic.

These are cool and will sound great on my phonograph. Just curious as to their value, though. Know of a good site?