How much for a used F-15?

With delivery of the F-35 joint strike fighter being delayed - possibly to as far out as 2018 - Israel is planning to upgrade some of its F-15's and F-16's, and to buy an entire squadron of used F-15's from the United States. Due to the delays, the IDF is working on a plan that includes upgrading its current fleet of legendary F-15s and F-16s that it had planned on phasing out, as well as the