I'm a fairly recent TH8, and I had to get a 5th builder. Yes, upgrades cost a fortune, but they also take an eternity. At TH7 I generally had a builder coming available at least once per day (tried to make it once per day). At TH8, even with 5 builders, I have many days when a builder is not coming available. This gives me a chance to build up resources for the next builder.
You have enough defenses at TH8 that having 2-3 down at a time is not a huge problem, especially once your defenses start to get maxed. I always try to keep good troops in my CC as well to help cover my out-of-service defenses.




