You could drive traffic to other social media pages/websites you own, sell advertisement space in posts or stories. There is a lot you can do to monetise a page depending on how much work you want to put in for the returns.
Majority of these shopify store have a contact us form or a support email. Contact them with basically a marketing/advertising proposal. You choose what you want to include in that proposal, things such as the Instagram page (obviously), the analytics, forms of promotion (story, post).
Your proposal is going to determine your conversion rate (how much people get back to you). So spend time creating one that's short with all the necessary information. You can easily turn them off depending on the way you approach them.
In the proposal, use perfect English & just make sure it's professional. If your sentences aren't properly constructed, they might view you as some scammer.
I wouldn't recommend stating how much you charge for the promotions in the first message. Get leads first.
These shopify stores aren't hard to find, I could find 100 of these fitness store within a few minutes & just copy and paste the propsal to them.
I would recommend sending out a limited amount of emails (or contact form) to start, like 50?
Lets say you send out 200 emails (or contact form) in a day and you get back 75 emails of persons who are interested. While that would be good. It's gonna be hard to get back to all of them quickly & taking too long to reply or post their ads might turn off a lot of people. Also posting 75 ads in a week might not be a good thing for your page in some way.
So start small and see.
You can fail or be successful with this method depending on the:
Quality of the Instagram Page
Way you approach them in the first message.
The price you charge
Anyways that's what I would try to do, there's other methods such amazon affiliate as mentioned above.
First rule is ALWAYS look at what your competitors are doing.
i.e. What is Cristiano Ronaldo promoting at 1M$ per shout out?
What are other sport celebrities promoting?
They already know the answers for your question.
PS: 200k with good engagement is BIG to make huge money.