At first I thought that quoting the total market cap of all cryptocurrency markets (or the big ones at least) would answer your question. But after reading agai

At first I thought that quoting the total market cap of all cryptocurrency markets (or the big ones at least) would answer your question. But after reading again I think that you're asking a different question and I'm not sure if total market cap explains it, or whether it's even possible to calculate. For a toy example, suppose there's only 200 coins of XCoin. Person A buys 100 coins for $1 each ($100 total). Person B buys the remaining 100 coins for $100 each ($10000 total). The total amount of USD put into the system is $10100 but the market cap is $20000. To get the value you're looking for I think you would need to get the cost basis of the last transaction for every coin in existence.