> Let's say there was a superconducting material that operated at atmospheric pressure and 25C. While waving the magic wand, let us also pretend it costs $1000/kg.

That depends, because you've under-specified it. Critical magnetic field and critical current density at the very least, probably also fragility on more than one axis.

Let's say it's got "enough" strength and critical magnetic field, and a density of 5 so that's $5000/litre. At a critical current of 1A/cm^2, fairly useless. At 10,000A/cm^2 that can make some neat medical equipment that no longer needs coolant that condenses the oxygen out of the air if it leaks.

It's been a while since I read about the idea — and this might have been an amateur blog rather than a serious claim — but I think 100,000A/cm^2 for reasonable density is enough to fly by pushing against earth's magnetic field?