[gibybo]

My figure was from http://coinmarketcap.com/ (look at the top)

I rounded down a bit to compensate for some of the lower volume cryptocurrencies and any potential issues with market cap that it might not be reporting correctly.

You can get to $30 billion just by taking the current total number of Bitcoin + Ether outstanding and multiplying by their respective token prices. Admittedly both numbers are inflated some amount due to tokens being unknowingly lost/destroyed, but I think we're still in the ballpark of $30B.

There is also a few hundred million (possibly low single digit billions) of venture capital in startups based on cryptocurrencies.

[chillwaves]

Do you think the price would hold if mass numbers were converted to fiat?

[gibybo]

Of course not, but that's true of every asset. Apple would drop from $790 Billion in market cap to a tiny fraction of that if shareholders started trying to sell their shares enmasse.