First you overestimate by assuming that all mined coins are sold. I think 80%+ are kept. Rerun all those number with only a fifth the coins for sale.

Secondly, judging by the bids that got filled recent crash, there was millions of dollars worth sitting in open buy orders. There may be many millions more that just didn't get a chance to be involved in that trade. My point -- bitcoins are starting to become really big, and it has attracted some people willing to put some serious money down.

$170 million in 5 years is actually a really small market on a global scale. Small businesses make that much. For a comparison that might be close to home -- Dungeons and Dragons brings in $1 billion a year. And yet, very few people actually ever spend any money on it. M:TG doesn't release their stats, but people have estimated it could be greater than $5 billion a year.

So if bitcoins only become as big as magic the gathering (which, lets face it, not many people have heard of), we may see $25 billion in the next 5 years. By your simplistic calculations, that would put the price of a bitcoin at > $3,000.