This is how it breaks down for me... a little over $800/mo.
Daycare...$500
Education...$75
Diapers...$30
Formula...$30
Baby Food...$45
Healthcare...$40
Insurance...$8
Wipes...$5
We probably spent about $1000 or so on one-time items (car seat, baby linens, swing, toys, maternity products, decorating baby room). Most of our stuff was donated (given by friends, or given in baby showers). The first couple months, diaper and formula costs were much higher.
Know what you can safely have used (crib, clothing, toys), and what should be new (car seat). If you're luck your coworkers will throw a seperate shower, and then you get more loot. Furniture is one of the most expensive items, and IMHO a total waste of money. For a changing table, I took a dresser we got from a flea market for $15, added a changing table pad and shelf thingie I bought from target. We also spent $20 on a white bookcase and maybe $20 on assorted storage bins.
If you get things used, check the current safety and recall information. Don't spend a lot of money on outfits, if you're lucky they'll get to wear it once!
Don't waste money on an expensive diaper bag. The ones you get for free from the Birthing Class and hospital are fine. We had an expensive one and we ended up using the free one all the time because it is lighter and takes up less space. Beleive me, with all the crapola you carry around for a baby that's an issue.
If you have two cars, check out the travel systems from Evenflo. The infant seat converts to a carrier and locks into the base in the car or the stroller. You can get an extra base for about $30 and keep it in the other car. That way you can easily put the kid in either car.