That's not necessarily true, rockets Cary there own oxygen, pure Oxygen can burn hot enough and oxidize enough to burn nontraditional things like steel and concrete, it would also vaporize toxic heavy metals and exotic foreign materials from the rocket itself.

I guess if the rocket hadn't disassembled itself, then it could be used again.
I think static fire is part of the testing to proceed to a launch? So, now they have to build another and static fire that as well in order to get back to where they should be.

Much less than if it had actually launched. It burns on the ground, when it blows up in the sky its just pollution. Not to mention all the "venting" that happens during engine relights and coast periods which just means dumping methane and oxygen.