Well, for housing, I'd just use the income guide. Really, lemme dig up a PHB, and give you my two cents.
Okay. A common inn costs 5 sp a day, a poor one 2 sp a day, and a good one 2 gp a day. I was going to go into how this compares with real-world prices, but that just happens to be a quirk in the area I live in; it might not be the same everywhere.
You could figure out how much housing is available, and base the price off that. However, in my experience, that's probably too much for an RPG.
Using base math, you could just multiply base prices by 30, and go from there - Common would cost 150 sp a month, Poor 60 sp, and good a whopping 60 gp a month. That's a bit flawed, though, since inn pricing includes food, house cleaning, and stables - and inns are built around the assumption that you kind of have to overcharge people, and you're only providing the housing service for a short period. Look at the modern day, and you'll find that the monthly rates of inns are not much better than renting a house, and the services provided are fairly lame.
So, using a bit of logic that the average worker would spend 1 silver out of every 2 maintaining his home, paying rent and whatnot (about right in my neck of the woods, probably less in yours, but since I live in a dock city, and you have a dock city, it seemed good to use my numbers), and the average worker's daily pay would be roughly enough to pay for a night at a crappy inn, I'd say the rates would be around 30 sp a month for a poor room, 90 sp a month for a common one, and 30 gp a month for a good one. Of course, that doesn't include food, and all the other "essentials" - since the character in question is probably "eating out", which gets expensive fast, I'd say that's a flat 2 sp a day, making it another 6 gp a month.
Anyways, that's my logic behind everything. At least at a basic level.
Now, for specific housing:
Student District: I'm imagining this would be dormitories, with a common eating area, washing area, and such. Bedrooms would be for studying, sleeping, and the other things that students do. Since your NPC is living with a lover, roommates are probably out of the question, which would hike up the prices a bit - old medieval dorms had something like four beds in each room, and even modern dorms have two to a room. The PC couldn't buy the extra bed, either - that'd mean taking a potential student away from the campus. A private room would be available, but that'd be pricey - probably in the realm of 50 gp a month or so.
I would say that a single bed in a two person dorm would cost around 30 silvers a month. Just a guess.
Working Class Neighbourhood: The character isn't buying a house, and is instead just renting a room. This shouldn't be hard, but she'll be renting it from a landlord who is unscrupulous at best. 30 sp a month is a good place to start, or 8 GP a month if you're including food and basic supplies (13 GP a month for two people). The room in question would be a single room, with a chamber pot that you'd throw out the window. Doors would be double or triple-locked with a deadbolt, and you'd be wise to buy a lock on your door. Don't trust your neighbours.
Prosperous Neighbourhood: I doubt you're going to find too many single rooms here, since most people have the money to afford a house. You COULD find some boarding houses, and maybe an older couple or two who have converted a child's old room into a suite for extra money. 90 sp a month (or 14 GP a month if you include food, 19 GP a month for two) is a good bet. In either of those cases, though, you can expect to have to deal with the landlord a bit more. In the boarding house, it's simply a matter of basic conversations, but in a rented room, you may have to deal with lonely landlords who may ask the PCs to "help out around the house". In either case, armour-weearing, sword-carrying fighters are not going to be looked upon kindly. Neither will a sorceress who cannot control her magical powers, I'd bet. A large damage deposit, probably at least 20 GP and maybe more, is likely to be required.
Slum: Basically, this would amount to living on the street. It should be more than easy to find someplace to squat, though there could be a few robber criminal lords who maintain squalid apartments that offer a modicum of protection. Again, it'd be a one-room flat, and probably not well cared for, either. If you are paying for the place (and this amount more to "protection money" than anything else), I'd say it shouldn't be much cheaper than living in the Working class neighbourhood - but the difference in price would be big enough to the people who are paying it. 10 silvers a month ain't much to any adventurer, but it's a world of difference to poor labourers. I'm going with 15 sp a month, or 65 sp a month for food (115 sp a month for two).
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Anyways, that's my basic logic and assessment of the problem. Hope it helps.
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