I think it'd probably be closer to 80 million/year (~35 million for Machado and ~45 for Harper), which of course is a lot of money to commit to just 2 players. However, it's feasible if the Sox are willing to increase payroll significantly and also because the Sox will have several players making league minimum or close to it for the foreseeable future.
The idea of adding 2 superstar hitters in their primes to the middle of the lineup is just so appealing to me. But it's probably not going to happen and I'd be more than happy with just Machado.