I thought I read somewhere that something like 1000 - 1200 coins = $1. That would make sense given the prices to buy coins at the coin shop - it would allow most of the value of the coins to be passed to creators while Tapas makes a certain margin also on coin sales.
Shadowcat your math is a tad wrong - if 20K coins = $20, then 100 coins = 10 cents, not 1 cent.
Maybe @STAFF can answer this question?