Jennix, just a wee bit of advice re insurance here. Two of my daughters have both myself and my dh as named drivers on their policies, which brings the cost of their insurance down, and also means we can help out if they need their car taken to garage, etc. So if either of you have parents who drive, check out the cost of insurance when adding them on. Also, strangely enough, even though both dh and I have been driving for almost the same length of time (40 years this year!), it actually makes a difference in which order we're added. It's cheaper if dh is first named driver, than if it's me for some reason.
As far as running costs go - if you do a lot of short journeys in a week totalling, say, 100 miles, that's going to be more expensive than driving 100 miles steadily on a motorway, so your idea of trying to be within walking distance of a nursery makes a lot of sense.
Once you've bought your car, it's also a good idea to put a set amount away (we suggested £500 to our girls) for any odd repairs, new tyres or whatever, that crop up. Try to find a good local garage and go back to them for MOTs, etc, and build up a good relationship with them. Recommendations from friends are usually a good start in finding a mechanic. If you go to the main dealer for servicing, etc, it's always more expensive, though you'll be expected to use a main dealer if you buy a car new.
Your running costs will include -
Petrol
Yearly MOT if over three years old
Regular servicing - don't skimp on this!
Insurance - shop around on the net
Don't forget the best quality baby seat/s you can afford.
Your local college may do a mechanics course that your dh, or even yourself, could go to, which would help to keep your servicing costs down. If nothing else, make sure you know how to check oil and water, etc.