I agree with this.
If you want to start small with as little startup costs as possible, register a domain, point it to a cheap shared hosting provider, and use a free script like MyBB, phpBB, SMF, or Flarum. Then as you get more popular you can migrate to paid software, which is Invision, Woltlab, VBulletin, and (sorta semi-abandoned) Xenforo.