"Premium" is highly subjective and will vary from person to person. A domain that I would consider a premium domain may not be a premium to someone else, and vice versa.
While some would be considered premium to most people (computers.com, cars.com, insurance.com, etc..) it's when you get into the grey area that people start to disagree.
As for price, I've gotten what I consider "premium" domains for a reg fee and/or a drop fee and as for how high, the sky is the limit (if there is a limit) - it all depends on the demand.