1300 today they say.
well that means the new 3600 coins generated as miner reward comes to a daily total of $4,680,000. so as long as more then $4.7mill of Fiat which gets put into exchanges per day then the price will continue rising because of demand (more then $4.7m) exceeding supply (3600 coins)
is there any way of tallying up the exchanges $ deposits easily, to see the combined daily dollar volume of bitcoin?
I suppose $4.7m would be the maximum required to absorb the freshly mined coins at the $1300 price level. But not all of the mined coins are put up for sale, so the fiat number could possibly be much less.
On the other hand, there would also have to be fiat available to buy any coins that holders decided to sell. That number could presumably be between 0 and 12m (or whatever the current coin supply is) depending on the day.
So while you can think of the market cap being supported by a certain influx of fiat, I would argue it is just one variable out of a handful of important ones, and not really too helpful as a model unto itself.