I have a trip from JFK-HNL-JFK booked with a stopover in NY then continuing on to BCN a few months later. I have a multi city HNL-JFK-BCN and then I made the JFK-HNL reservation to compete the first trip. It seems for my time period at the end of October 2012, that there are only 60,000 mile awards available. What are my options?

I could book the 60,000 mile award, but I only have 80,000 miles left and would have to purchase miles. That seems cheaper than buying a one way ticket for 2 people. Should i wait to see if they open milesaaver awards for 20,000? Will they even offer the 20,000 awards later on? If I book the 60,000 award now, and a 20,000 becomes available, can I change it? Any help is appreciated.