Your OP says you don't drive, and I presume from your questions you can't drive?
In which case unless you can learn very quickly using an intensive course (and presuming you already have your theory test done, or there is no chance, as you'd need to book your practical very quickly) first insurance might be very dear whatever your age. If you live in a low crime rate that will reduce it, as will adding a partner if they have good no claims etc but only if they will actually drive the car and only as a named driver or it's illegal, but from December it will be illegal to offer women special rates. This was common practise up to now, women always got cheaper rates because they are less likely to show off/joy ride/crash, but it's been branded discriminatory. I can't drive due to medical problems but am insured as I was learning, had had a few lessons and have taken my theory - my practical was days away. My insurance will rocket. I'm not a teenager, either, so I didn't expect to be too affected. I will be, even with OH's 6 years no claims.
I'd look at models you can afford, look at the tax band (its around £200 a year to tax a 2009 Mini, for example) and run some insurance quotes using your address to see how much it would cost. Remember the cost will go up by a few hundred if you pay by DD. Then petrol wise....a few trips a week will probably cost around £20. You are likely to drive more than you currently go out though, because it's so much easier to drive somewhere than to use public transport.
Repairs...OH drives a pretty new car at the moment. It's got MOT for life and recently had it's first MOT. We've paid quite a bit in repairs. Not falling apart things, because it's new, and it's never failed its MOT, but the window froze when it snowed last year so that was £70 to have fixed so it could move again, one tyre burst so that was £160, the brake pads will need replacing soon (around £400 at the dealers, which he'll probably use, because it's got full dealer history). He's had the brake lock replaced three times over two years because the rattling bothers him hugely, the first was free, second and third were £90 each.
Remember to factor in things like new tyres, de-icer, air freshener, and a good car seat that fits the car for your DD.
Once you've worked out the tax/insurance/buying cost, see what you've got left each week, and how much you could save towards repairs. Do you have any savings you could dig into if you needed too? Then you'll see what you'd need each month, realistically.
HTH :)