If the going rate for the average developer with skill in the technology
is N, it doesn't follow that offering 2/3N will get you a developer
2/3rds as good as average. Experience and anecdotal evidence suggests
to me that you're not going to hire anyone who has any ability in the
technology at a rate below some floor. If that floor is 3/4N, paying
2/3N will get you no skill at all.
From a practical standpoint, as a project manager you can't expect to complete
on time with a product of lesser quality with a team of underpaid developers. You can simply expect the project to fail. If you happen to be the one well-compensated developer on a team of cheap programmers? You're not going to do just
a larger share of the work, you're going to do all the work. If
you're unlucky, you'll get to re-do the work of the other team members
as well.