One could create a function to figure out an approximation. For instance, you know that once it reaches $4000, then it would be more expensive to buy it. Same thing with each dollar it climbs. You could say it would cost 4 million to reach $10,000 a BTC, or you could say 50 million. One is more accurate.
It is really hard to estimate the real transactions that are being carried out in bitcoin, you can view a partial summary with the total amount of trades being done in public exchanges and that is not an accurate estimate as there is over the counter sales which deals in millions of dollars worth of transactions being done privately on a daily basis, when the price of bitcoin was $10k the total market cap was close to $200 billion, we need more these investment from hedge funds and other financial institutions to see those levels again.