A software marketing person who creates estimation for the software projects through bidding and client interaction may decide the cost with the relevant discussion. The big honchos in this field are the best suitable guys in achieving business tactics. Again it depends on the client as well as on the project doing person how he deals with client too.
Among many factors, it depends on the competition, how many indexed pages there are already, how well optimized those pages are, and where you want to rank.
I am interested in this as well. I have a client who wants to be on the first page of a Google search for a heavy traffic keyword. I originally quoted him around $500/mo for one year, with results showing up after 3 months of working together.
Hope it helps. I would actually be curious to hear some more numbers thrown around, if I may be as so bold as to request such a thing!
It is depends on the amount of your keywords, tha competitive extent of your keywords,the serch engine placement you want to reach,the time you want to optimize,etc...
It really depends on how big you want to get. Major companies have spent over 100k to launch a new product on the internet, while little mom and pop companies spend only a little.