The con rate is $89 a night, up to six (eight?) people (if we're to believe the Marriott website. Which we should, since that's where we generally reserve from XD;;)
Assuming you stay the nights of the 3rd and leave the day after con on the 7th (so you stay the nights of the third, fourth, fifth, and sixth), you're looking at $356 total, plus any fees and charges the hotel decides it wants to place upon you (I don't know what we're looking at in that sort of expense, so I'm going to omit it).
That means that for four nights, split between...
• two people would be $178 per person
• three people would be $119 per person (actually $118.67, but shush)
• four people would be $89 per person
• five people would be $71.20 per person
If you're not staying the last night (say you live in the Portland area, and don't have to catch a plane back on the seventh like me), or you're starting your stay the first night of con, your hotel will be a base price (sans fees) of $267.
That means that for three nights, split between...
• two people would be $133.50 per person
• three people would be $89 per person
• four people would be $66.75 per person
• five people would be $53.40 per person
If you're only staying two nights because you live in the Portland area and can afford to bring very little with you to con, your cost would be $178.
That means that for two nights, split between...
• two people would be $89 per person
• three people would be $60 per person (actually $59.34, erring on the side of having too much money =3)
• four people would be $44.50 per person
• five people would be $35.60 per person
I'm sure you can figure it out on your own if you plan to have six, seven, or eight people crammed into one of the little hotel rooms, or if you're only staying one night, or whatever your other logistical problems are.
Don't forget that many hotels add a $50+ surcharge for electricity, housecleaning, what-the-heck-ever, plus it's always a good idea to leave a tip for the maid, if you choose to let one into your room during con (not necessarily the smartest idea, so I've been told), so you're going to have other costs it'd be wise to split. In any case, hope that helps clarify a bit ^^v