Rat Help?

[PlayingPretend]

So assuming everything pans out financially, I'll be getting a pair of rats sometime in 2010. I did quite a bit of research early 2009, but my memory fails me. That being said, yes, I am a college student approaching her second year of university, but I will have an apartment with two to three other, consenting people this coming year. Should housing ever fall through, I attend a local university and would be able to house the rats at my place where I would be paying my sister to look after them the three days I have school.

I do have a few specific questions pertaining to the following: annual costs, cages, food and gender, in addition to anything else you feel I should know before investing in a pair of ratties. I should also mention that I will be buying from a breeder as opposed to a pet store, as I dislike the condition of most of the pet store rats in our area.

Annual Costs - On average, what's the monthly amount I'll be spending on my rats? Feel free to give me an estimate for how much your pair/rats initially cost, however, that's an easy enough figure, so I prefer hearing from rat owners how much they spend per month on their babies.

Cages - My sister has worked with Martin's Cages before, and, secondhand, so have I; they're a pain to put together, but are they worth it quality-wise? What are some of my other options? How large should a cage be for a pair of female rats? A pair of males? Do you recommend litter training, or would it be better to line the shelves of the cage with cloth that can easily be thrown in the wash?
Note: I realise there's a special bedding that must be used. I'm mainly concerned about the possibility of litter training and/or whether or not I should line the shelves.

Food - I've been eyeing up this food. What are your opinions on it? Is there anything better you'd suggest?

Gender - Do you prefer male or female rats? Why? What are the pros and cons of each?

Some of the resources I've gathered are:
GooseMoose
Rat Sauce (Breeds)
Rat Sauce (Games and Toys)
Varieties
Dapper Rat
Rat Care Information (General)

Any other helpful resources? Tips? Experiences? And most importantly, feel free to share photos!

Thank you all in advance!