Ahhh!!! Very good question! I had to do this little exercise in one of my college course about dog biology and pet nutrition - forget which one. It is so goof of you to think about this ahead of time - most people don't and then some need to re-home their dogs when they find out they cannot afford one.
Here are the basic costs:
Initial veterinary exam and shots: may be free if you adopt from a shelter, but in general, expect to pay about $100
Dog toys, chew toys, treats: $50 (more or less initial cost)
Crate: $100 (more or less, depending on type and what size dog you get)
Dog bed: $50 (more or less)
Dog license: $15 (more or less, depending on where you live and spay/neuter status)
Spay/neuter: $200-400 (look for a low cost spay.neuter clinic)
Food: $50 (per month or so)
Leash and collar: $20 (more or less)
Bags to pick up after dog (free or minimal - use plastic grocery bags or other small bags)
Boarding for vacations, etc.: $10-15 per day
Training: $100 (average at pet store for basic 6 or 8 week class - more or less, depending on quality of training and location)
Unexpected veterinary expenses: $500 - $2000 per year (not all years the same)
Did I miss anything?
Hope this helps! Sorry, I do not know how to convert to pounds.