You are right, 4.5 million is a bit more than a few months worth of lease payments, but given the thread is about alliance's purchase of a bunch of jets for 15 million the comparison is a bit of a sideways one.
Nevertheless, 4.5 million ready to go is still about a 10th of what you would pay for a new jet so not a hugely different argument.
A new CF34-10 would come close to 4.5 mill I suspect..