Probably the stand-alone unit would cost more, especially with energy prices rising (though I guess Cambridge won't feel that until 2024 if you're on the community aggregation). Department of Energy standards that go into effect for 2025 note that portable AC units are actually only doing about 70% of the cooling that was previously assumed - and they were already considered horrendously inefficient. Consumer Reports notes that a portable AC unit will take three times longer to cool a room - and three times the electricity in the process.

If you're spending $50/mo on cooling and you're suddenly using 3x the electricity, you're then using an extra $100/mo. Even if it's just double the electricity, you're still going to eat through an extra $150/unit over the summer.