In my personal experience from B2B start-ups.
The best time to start building a brand is from day 1, I know this sounds cliche but let me elaborate:
Three key components through which you can build a brand without spending too much money:
a. SUPER Duper Customer Service and Support. That is the best and the cheapest thing you can do to build a brand for your early stage start-up from Day 0-1. Pick up calls within 2 rings, respond to emails within 5 minutes, resolve issues within 30 minutes.
b. Next stage is: Killer Messaging
When you start selling in the open marketplace through Cold Calls and Email Campaigns:
Focus on messaging on your website. Have a very clear value prop right on the home page with a 60-70 second professionally done video and use services like TechValidate to get Customer reviews on.
c. Stage 3: Spread your wings. Become a thought leader.
Lead your industry segment by producing insights and truly thought provoking content. Participate in smaller focused conferences/seminars where your target audience visits,