I recently reserved a motel room in Eugene, OR by speaking directly with the manager, who took my credit card and then send a confirmation email. The confirmation email listed all the dates and prices, just as we discussed, plus rules on cancellations. At the top of email was "confirmation".

A few days later, but before my arrival, the manager told me the price would be higher. My credit card was not charged.

Can a motel demand a higher rate than what they confirmed?
At what point is a 'contract' formed?

Thanks for any thoughts.