You can go to the big houses however I recommend Roger Brun. He runs a B&B, and gives away free Champagne like it's water. If you stay there, expect to have to drink at least two bottle before bedtime! He also will give you a real and honest version of how the industry runs. The large houses are very corporate. You won't get a tour from Roger Brun, but his Champagne is excellent, and much better value and tastes better than a lot of more expensive ones.
As an indication, we have stayed with him twice, and each time brought back 10 cases or so. His Rose is the best Rose around.
JMHO.