I have lost 10 A380s which where completely full at extremely slot tight airport cancelled by the lessor. They were in nowhere excessively cheap and they were from one of the largest companies on the world. This cost me million in lost loads across the network plus the extremely expensive seats on those planes and the fact that i count recover most of those slots.
Nowadays I only have close friends as leassors as I simply don't trust others. I suggest you also built relationships with your lessors. You won't just get cheap leases but you will also develop trust in each other. For a lessor there is nothing better than a trustworthy leese and for a lessee there is nothing better than a trustworthy lessor.