If it were the case that this was normally a group of freelancers making a killing, charging high consulting rates, it would be different. But almost in all cases they are using 'freelance developers' because they cannot afford to pay market rates in the US and can't afford benefits. Even in those other countries, there is a global economy. Those developers might be doing OK, but they are not getting wealthy.
If you try to do it as if the developers are separate and not a core part of the team, that can't work either. Either you acknowledge how critical they are to your business or you just take advantage of them and hope they don't find something better and your business doesn't fall apart.