Many frequent flyers treat miles as a form of currency, and we set personal "rules of thumb" in deciding what they're "worth." For many people, a figure of around 2 - 2.5c in equivalent value is a benchmark. In other words, if a ticket requiring, say, 100,000 miles as an award would cost more than $2000 - $2500 to purchase, we'll say it's a good use of miles. So many of us would say that 90,000 miles for a $2500 ticket is a decent deal, with the miles having a value of almost 3c each.

HOWEVER, I don't know where the $2500 figure for a purchased ticket is coming from. Throughout September round-trips in first class between NYC and Seattle can be purchased for $990 - $1300, using American, Alaska, Delta or United, leaving from JFK or Newark. So I would be very reluctant to spend 90,000 miles on a ticket where the "value" might end up being 1-1.5c rather than 2.5c or more. And remember, you'll earn miles by buying the ticket.