The best thing about WordPress is that you can do pretty much anything you want without spending any money. However, it will cost you in time.
You can however save a lot of time and get better quality by spending a few bucks. You can go to a place like http://www.worldclasswebsites.org and a well SEO'ed site with everything you need in one place or you could install it yourself and go pick a good theme from http://www.woothemes.com/ or http://www.elegantthemes.com/ and some plug-ins from http://wpmudev.org.
So, I guess the answer to your question is... it depends. If you want a premium custom design and the best content writers it will cost you $1000's or you can do it all yourself and use free themes and plug-ins which would cost you $0.
The middle of the road should run you between $200 and $500 for a really nice site where you do most of the content writing though.
Hope that helps.
The cost of a WordPress website defers according to each and every web host. Every web hosts provides various hosting packages. These hosting packages defers with features and cost.
For example you can have a try at http://www.Tucktail.com/ This web host provides 3 different WordPress hosting packages such as Economy, Deluxe and Ultimate. and the cost varies for every package. You can visit this site to have a clear idea on it.
If you want blog on wordpress.com it costs nothing. May be you will need some money for content (if you not create it youself) and for seo.
If you want website with your own domain name (as yourdomain.com) you need 10 $ for domain name, 6-7 $ monthly for hosting, wordpress theme (there are free and paid themes) and money for content and SEO
Try yourself, then you will get to know why people say its the best wordpress seo plugin available for free. Go here....
it depends upon the scenario, Sometimes it only costs a couple of hours and sometimes it costs more than a couple of Thousand Bucks.
I would like to know price of 10 pages with SEO optimization!