I would also recommend the team to make accounts in various social networks (Instagram, Medium) and try to attract users there. It is not very effective, but it does not require costs.
Not quite agree with you. Yes, it is not so expensive, but still it needs money. In addition, forum advertising is very narrow, which is a great advantage.
But after all, the SMM campaign can be customized in such a way that advertising will only appear in people who have similar interests.