It depends on your definition of "money".
This strange stuff called money is managed and measured by the Federal Reserve in the United States. There are two primary measures that the Fed uses when describing the money supply, M1 and M2. The M1 is composed of all of the checking account balances, cash, coins, and traveler's checks circulating in the economy. The M2 is composed of everything in the M1 plus all savings account balances, certificates of deposit, money market account balances, and U.S. dollars on deposit in foreign banks. The M1 is mainly used as a medium of exchange, whereas the M2 is used as a store of value. The M2 is larger and less liquid than the M1.
http://www.netplaces.com/economics/the-story-of-money/m1-and-m2.htmI think M2 is actually a better measuring stick for what BTC represents because it also speaks to money as a store of value.
Best guess I can come up with for GLOBAL M2 is around $55 trillion. I'd suspect it may inflate over the next 5-7 years to, let's say, $65 trillion. I can't remember what the BTC emission schedule looks like, but let's say there might be 17 million BTC by then. Total money supply in BTC, theoretically, would be 3095238, or roundly 3,100,000 BTC. I'd say 1% is pretty aggressive, given that most of the world's population may not be capable of storing or transmitting currency in that way. But 0.5%? Maybe a little less? That gets you to a valuation of $15,500.
The other thing to consider is velocity. I've read that people believe BTC's velocity to be similar to that of USD. In my view, they are including mining transactions, which don't belong in the velocity discussion any more than it's a measure of velocity to have fiat coming off a printing press. My guess is that BTC velocity will grow into a USD-like velocity, possibly slightly slower, which would grow velocity by an estimated 5x. That gets us to a valuation of $3100.
This is long-term thinking, nothing related to price today, but I have not batted an eye at buying more and more as the price has dipped under $500. A lot of things can happen. The adoption trendline could accelerate or decelerate. My pulled-from-ass guess about velocity could change. But I think a 2020 fair value for BTC might be around $3100. (Yes, I've done this before and came up around $2400, but I didn't factor in M2 inflation, which will, I believe, continue.)
I don't expect to retire on 20-30 BTC. But if that investment grows from $10K-$15K to $60-90K, it is still a lot better than many other investments I've made.