For both options, of course it depends which brands you use. I am still diapering my 4th baby and have used both cloth and disposables. Here are my estimated costs:
cost for disposables
1 box from Sam's ~ $34/month
x 12 = ~ $408/year
*cost for cloth
2-3 dozen diapers ~ $30-$60 (about $15-$27/doz. depending on quality, fabric, etc.)
4-6 velcro covers ~ $52-$78 (I like Bummi's Super Brites) (no pins - just as easy as disposables!)
Altogether, you spend less than $150
If you only used cloth for 3-4 months, you break even (though you could still sell the supplies at more than 50% of what you spent). In one year you save a couple hundred dollars. Yes, you do have to wash them, and that does cost a bit more than your regular washing. But you will also be able to use these diapers for at least another year. Saving you at least another $400! Then you can use them for your next baby!
OVERNIGHT: If you choose to use cloth overnight, you will probably need some extra absorbent inserts or a special absorbent cover. If you choose to use disposables for overnight, you can still save a lot by using cloth during the day. In fact, I think this may be my favorite option. It is also nice to use disposables for long outings, though many families are not bothered by using cloth while away from home.
*for a baby 15-30 lbs. For me this will last from a baby about 4 months old to about 2 1/2 years old. If you choose to buy cloth for a newborn you buy supplies for the 6-15 lb. diapering supplies which you cannot use as long, but you can reuse for your next baby, or resell when you are through with it.