This is also explored here in greater detail. If you find someone with 1m, that person would have 0% cost. An (almost) saturated pool with a 0% margin has also very little cost (i.e. 1%). That guy would indeed have a small benefit from delegating to your pool. Everyone else, would have little incentive to do so because they’d have > 30% cost. You would likely be worst off, because you also take the > 30% hit on rewards, but on top of that you’d still have to pay for the pool’s running cost.
All in all, this “first come takes all” model will probably not work out so well. The best I could come up with (so far) is an egalitarian approach, where the pool owner is on equal terms with the delegators (i.e. everyone gets the same). The running cost of a pool are not zero, they too are shared equally.