I think your math is a little wonky. From 2010 to 2011 was a 50% increase in price with no corresponding duration increase; From 2011 to 2012 was a 50% duration increase with a 100% price increase.
He was suggesting that if price increased $50 per year, then this year it would be a 2-day event for $200, or $100/day. Then, since this year is a 3-day event, $100/day * 3 days = $300. Or, to look at it another way: the cost per day went up $25 between 2010 and 2011. If we assume the same increase per day this year, then $300 makes sense.
Percentage-wise it doesn't work out, but there is a (possible) method to the madness.
