Currently the record price is the PSA 10 Pikachu Illustrator, at $16.5 million.
How much higher can it go?
One possible upper limit is that of masterpiece artworks. The most expensive publicly sold artwork is Salvator Mundi (possibly by Leonardo Da Vinci), which sold for 450 million in 2017. [Wiki] Pikachu Illustrator reaching this would be a 27x increase.
Works on permanent display that never go for sale are valued/insured potentially much higher. The Mona Lisa is likely insured for at least 1.1 billion (67x Pikachu) [Same wiki], although this number is based off just the insurance in 1962, accounting only for inflation but not the massive gain in masterpiece artwork auction prices. I personally think the Mona Lisa price should be much higher (compared to Salvator Mundi), so let’s say 10 billion (600x Pikachu).
Another possible upper limit is the networth of a single individual. These days that seems to be Ol’ Musky, at 800 billion (48,000x Pikachu).
What if a whole country comes together? If Japan Wants Pikachu Back, and pools together its whole GDP for one year, that’s $4.5 trillion (270,000x Pikachu).
Beyond that, we might imagine that some superintelligent AI or alien invaders gain command over all the world’s material assets (real estate, stocks, wealth etc.). This is hard to estimate, but a number I’ve seen online that seems plausible is 500 trillion - 1 quadrillion. (30,000,000x - 60,000,000x Pikachu).
So, inflation adjusted, it seems that there is at least one card (PSA 10 Pikachu Illustrator) that can only go up in value by at most 60,000,000x.
This in turn places a bound on how much weekly growth is possible. What weekly percentage-growth rate would reach that 60,000,000x in two years? Answer: (60,000,000)^(1/104) = 1.188, i.e. 18.8% / week.
That is to say, the following sentence must be false: “For the next two years, every pokemon card will go up by at least 19% every week.” If that sentence was true, then the price of Pikachu Illustrator would surpass $1 quadrillion, which is a literally impossible price to pay with all of humanity’s resources.
We can therefore conclude that its logical negation is true, i.e. :
Within the next two years, there will be at least one week where the price of at least one card (Pikachu Illustrator) increases by less than 19%.
…..