There is no average. After more than 20 years I can tell you it is a "crap shoot." I have had a dog finish in 7 shows, and another who at age 5 still lacks 3 points. Yes, it is aggravating. This is why I am grateful that Labradors are such great dogs to do other things with, as well as such great companions.
Oh and if someone can tell you how many shows on average could they please send me the winning Lotto numbers?
Now this is a loaded question.
Could be 1000 or more if it's a poor quality dog.
Could be 3 if it's THAT good.....
Also depends on where you are showing the dog.
Some of the specimins I've seen with a Ch in front of their names that finished or came from those parts of the country where it takes say 8 dogs for a major, well, they just aren't going to be the quality of the regions that have more dogs.
So, it would be easier to finish a not-so-good dog in those areas, when it might be impossible to do it in the bigger areas.
So what do you really have if you buy a championship?
I always wonder why they would be so highly regarded knowing you could get one going up against so few dogs. That was a good point. It is a crap shoot. Some shows surprise you and your nice dogs and others you wonder what happened. But does involve some politics. Depends on your area and if you keep the dog out while it is really looking good. Some seem to have a time and then its gone. But from 6 mos. to 6 years to answer your question.
Think if your dog is ready between 2 and 3 years of age and you have him at 20 plus shows with no hope in sight for majors on him, may be time to reevaluate his ability to become a Champion
Ok, another take on this. Dog showing, for most of us, is a hobby like golf. How much does a golf fanatic pay for his/her clubs? How much for a round of golf? How much for golf club membership? How much for golf magazines? ETC.... Then when you lose interest in golf all you have are rusty clubs, but if you decide not to show your dogs any more you have phenomenal companions for many years aka PRICELESS!
You forgot the new clothes to show in, the new shoes to match the new clothes, the new car to take the dogs to the show, the new GPS to get you to and from the showgrounds without getting lost....