funds needed for spouse visa

[Assist_ark]

Hi guys,
Please, can somebody help by telling me approximately how much I or my girlfriend (soon to be my wife) has to have in our account, to pass the maintenance fund requirement?
To give the background story: I'm a recent graduate who hasn't started work yet, since I overstayed and had no work permit. So I left the UK to my home country, since my girlfriend and I wish to get married.
Now, the job she's currently doing pays her just over a £1000 monthly. The only expenses she has at the moment are just phone bills and instalment al payments for both her overdraft and credit card.
We satisfy the other requirements so far to the best of my knowledge and we have been given a place to stay (accommodation) by her parents. Which brings me to my next question. How do we show this in writing, proof that we have accommodation?
Thanks in advance. Hope I was clear enough.
All replies appreciated.

[XnailaX]

You need to show that after paying rent or mortgage, council tax and any credit/loan repayments you will have at least £102.75 for you both remaining weekly. This is assuming you don't have children to support.

[Assist_ark]

Ah, this is good news, I think. By the way, thank you so much for your reply. Much appreciated. If my calculations are right, we'd have way more than £102.75. The accommodation is close to free (we still plan on paying a little sum of money), since it's provided by her family.
My question: do we now state in a formal letter, while attaching a bank statement, stating all the expenses going out and income coming in or they'd know this from examining the statement?

Second question: since we aren't exactly formally renting a place, how do we show we have/proof we have an accommodation. Do we do this by telling her parent to write a formal letter stating this or get them to give us a copy of their proof of house ownership (because they own/bought the house)?
Thanks in advance!