Getting to a number one position could cost a boat load of money, and it's likely to cost you consistent time, money, and effort once you get there, so you'd better be sure that number one spot is going to pay off.... Generally once you hit the first spot most of the work is now done. Mainting the spot is much easier.
Getting to a first spot position is pretty easy for a good
SEO person with a lot of real experience if the company paying them will leave a lot of room on the credit card. It's about good decisions and not wasting money. $100,000 in the hands of the wrong people could get you nowhere. Budgets are tough to determine, but I have had my best results when the company had full trust in my decisions and allowed open billing.
For a tough industry or keyword, it could take a year to work - but it works.
Believe it or not, I have had clients who did not know what to do once they got there...