We sure are. There's been a significant amount of research on this and there's a vas number of mined materials which will peak within this century.

Only if you assume that accessible minerals are restricted to those that can be found on the Earth, which is not the case.

Explain to me how the energy expenditure required to extract minerals from out of orbit will ever be accessible considering the energy cost of exiting the Earth's orbit.

Getting from Earth orbit to Solar orbit is cheap but slow with solar sailing. And the pure energy cost is not that high in getting up to Earth orbit, just 33 MJ/kg (need another 32 MJ/kg to escape Earth orbit). Rockets are of course very expensive, but mass production would change that. And there is the possibility to bring material from the Moon to build stuff in orbit before a metal asteroid is captured, so everything doesn't have to be lifted from Earth.

The good news is, we're also approaching (or have already experienced) peak demand for a lot of things. The root cause of demand, population, is set to peak later in the century.