I've accumulated a substantial number of miles (over 70,000) these past two years flying round trip Tel Aviv/New York, and I'm trying to figure out what it takes to upgrade an Economy ticket to Business class.

As best as I can figure out (the Continental site is difficult to decrypt), I need 30,000 miles for each direction to upgrade. Am I missing something here? Can I buy a (relatively) cheap economy ticket and upgrade it to Business class which costs at least twice as much, with just 30,000 miles, when to get a regular economy ticket free would require many, many more miles?

If anybody has any experience at this, I would appreciate an answer. As I say, the Continental site is not very clear about this.