The original reservation I made was for a single with one king bed at $90 a night. I've been offered to upgrade that to $120 a night for a room with two doubles, and I believe I'll be taking it. That means that for 6 people staying in the room per night, the cost is $20 a night, or $80 for the whole con - compared to $14/night and $60 for the whole con.
Seeing as we plan to have some events in this room and are also wondering how the hell we're going to fit everyone's stuff in, I am going to go for the upgrade. Hope this is fine with everyone - it's still a steal, I think.