The non-refundable ticket with trip insurance is going to be your lowest cost option. Be sure to understand for what type of events the trip insurance will pay, they only cover specific issues.

Be aware the airlines charge a significant fee to change a non-refundable ticket. You can apply the value of the ticket to a future trip, but you will be charged for doing so. The fee is likely to be $150-$250 per ticket for making a change.

Sometimes a good strategy is to purchase tickets later in the season, closer to your departure date. With the economy still in the doldrums, it's unlikely ticket prices will rise much as we approach summer. Though with fewer flights on the schedule, there is a chance of not getting seats on the exact flight(s) you prefer.