A breathtaking amount of money
The current version of the question is asking how much it would cost to remove 99% of the plastics in the world's oceans in 30 years. From this we conclude that an organized effort is being made to remove the plastics.
A plastic bag was found in the Mariana Trench, 11km below the ocean's surface. According to a survey of the Pacific Ocean, the highest levels of plastic are between 200 and 600 meters below the surface. So we're not just scooping stuff off the surface, we're netting most of it below the surface. And some of it is deep. Let's hope that the last 1% is below the 1.5km line. Here's why:
fish plastic out of the ocean
We know that commercial fishing trawls between 240 and 1500 meters. I assume it's not that hard to trawl between 0 and 240 meters, it just isn't where the fish is.
In the U.S., commercial fishing employs approximately 1.1 million people and has 155 billion in sales. I'm using the "take fish from the water" estimates to help us understand what it would take to "take plastic from the water."
World-wide commercial fishing costs are hard to come by. I found one article from 2018 here, but it's numbers for the U.S. are SO FAR BELOW the government-reported numbers that I stopped reading it. Maybe in the five years between that report and today fishing profits have risen 340X. But I doubt it. To be fair, I have limited time today and only sped-read the article. I could be wrong about the conclusions it came up with.
The U.S. isn't the largest commercial fishing nation in the world by a considerable degree, but as one might imagine, neither China nor Japan are releasing accurate data. So, as a round (and nearly irrelevant) estimate, let's 10X what the U.S. is taking in. 1.5 trillion in profits.
And if you think reported profits are scarce, accurate reported costs are next to impossible to find. So, let's use a common retail profit margin number: 40%. That suggests that in one year the cost of taking fish from the water commercially is about 930 billion U.S. dollars.
The last number we need is, regrettably, very subjective. An accurate assessment of the decrease in available fish in the sea is horrifically complex and based on far too many variables (although good for them for trying to account for all those variables). It doesn't help that the issue is terribly politicized, with advocates of fish-baby-fish showing the world replete with fish and advocates of we're-doomed! showing the world about to lose every fish in the ocean. In a sense, they're both right to a degree, but the we're-doomed! camp is likely more accurate than the fish-baby-fish camp. Let's set the politics aside.
Heather Patterson, writing for the Australian Fish Stocks Report, has the following to say about Southern Bluefin Tuna:
Roughly speaking, in 70 years we've depleted the bluefish tuna by about 95%. Close enough for government work, as they say. We need to deplete the plastic in half that time.
Putting all that together to get an estimate that's so rough it will make angels cry
Why did I go to all that effort? It didn't take much searching to find an estimate of 150 billion dollars to "clean up ocean plastic and environmental pollution." But I think that's low. Really low. Worse, if you read that article, there's a lot more going on with that 150 billion than just pulling plastic from the ocean — assuming that pulling plastic from the ocean is even on their list of things to do.
So my goal was to come up with a way to rationalize a number. I used the world-wide commercial fishing industry to model the idea. It's rough. Really rough. And I'm sure there are people who can poke holes in the idea (not a bad thing, if it leads to a more accurate result). But what I came up with was this:
\$1.86 trillion U.S. dollars.