I'm curious what people would estimate is an actual reasonable cost for egress? As in, what it costs to provide that service plus a sensible margin?

It seems to me that eventually it will come to pass that competition regulators start to look at this. For now there's enough of an appearance of healthy competition that they probably aren't interested. But below the surface what they should be understanding is that these are highly anticompetitive mechanisms being deployed and the complexity of unwinding it later on may be such that intervention is justified much sooner than would ordinarily be the case.