I almost always save miles for long flights, like to Hawaii (we go every other year and have never paid for a ticket). I find that works best for me.
I'd suggest getting on flyertalk to gain some knowledge. Never have I used miles for such a cheap flight, though.
For example, I got us first class from DC to Honolulu next June for 40,000 miles each one way (all 4 of us, although DD and I are going over two weeks earlier since we're staying twice as long as the boys are). They would be roughly $1300 each.