Get yourself a Bentley manual, its the best for your car:

http://www.bentleypublishers.com/product.htm?code=b305

You need 7 quarts of oil (Castrol or Mobil synthetic).
The filter canister is on the front/top of the engine, just behind the fan.
You need a 36 mm socket to remove the canister top.
There is an o-ring for the canister, and washer for the drain plug - they
should be in the oil filter box.  Mahle is OEM, Bosch and Purolator
also good.
You need to remove the bottom engine cover - phillips screws at the corners.

FloydR

Filter Kit ~$10
8 quarts full synthetic oil ~$40

The question you need to ask yourself is: How long is your husband
willing to work and how dirty will he get, for $50.

Personally, I do it because I like to.  It's recreational wrenching.
But then, I do a lot of other repair type things to my cars too.

Y(Husband's)MMV

If you gotta ask ...

Sorry.

The filter is in a can that lives right on the front of the motor, just aft
of where the huge coolant hose goes into the motor (it really comes OUT of
the motor at that point, but I digress). There is a 13mm bolt in the lid
that you will remove. The lid comes off, the filter comes out, the new
filter drops in, then it gets hard.

The filter is in kit form, and includes two steel washers and two o-rings.
The very tiny o-ring goes on the bottom end of the long bolt (the 13mm that
holds the lid on), and the very large o-ring goes around the top of the can
to seal where the lid fits. The two steel washers are a bit tricky, they
"look" to be the same, but if you look closer you will see that they are
different. One of them goes on the 13mm bolt between the bolt head and the
lid of the can, the other goes on the drain plug at the very bottom of the
engine.

Your engine takes 7 quarts of motor oil, most oil change places advertise
prices based on 5 quarts. You must be sure they actually use 7 quarts, or
you need to use 7 quarts if you change the oil on your own.

$100 to change 7 quarts of oil is a bit steep, at $2 per quart, you need 14
bucks, and the filter costs about $15. Materials run around $30 (filter and
basic motor oil), and reasonable labor for 15 minutes of work is another
$15, tops. Anything more than $45 to change the oil is highway robbery.

Here's what I would do -- assuming you guys really haven't the skills or
time or whatever to change the oil. I would pull out my Yellow Pages and see
if there is an independent BMW Service Center in your town. I would let that
guy do the oil changes, and then also use him for any other service you may
require that is not covered by the factory warranty.