I work with influencers in a busines (PR Marketeer); my advice;
Send an email to PR agencies in your neighbourhood they will connect you with businesses that look for people with your profile and set up a collaboration like this, not garanteed.
If you are really interested in something (brand, product,…) message the business on instagram, email,… they will connect you with the PR department and then if you met their requirements they might want to collaborate. It is a trial and error. If you are into something niche (home renovation, books, games,…) 20K is around the minimum requirement but totally possible.
Also big tip don’t overdo it. It is better to keep collaborations with smaller brands to a minimum, a bigger brand/premium brand, prefer not to work with someone who has too many collaborations.
Keep trying and good luck~