and the cost varies enormously.
A 15 page site could cost £1000 or it could cost £20,000 - it's just not possible to put a proper figure on a project without knowing a lot more about the business and its requirements.
If you buy Dreamweaver, or Adobe GoLive, or MS FrontPage 2002 you could spend some time getting to know the software and produce your own, perfectly respectable site. If you don't have any experience - either with the software or with web design concepts - you could end up spending a lot of time and still not being happy with the results.
In my opinion there's a world of difference between a DIY site and a professionally designed one, but I would say that wouldn't I?
Whether you do the work yourself, or get someone to do it for you the copyright will be vested in you - after all, you'll be paying for the owrk if someone else does it. When I design sites I normally transfer copyright to the client once the final payment is received.
Maintenance costs vary. In my company we charge a fixed amount per quarter for web-mastering, and that includes minor text changes, uploading fresh images, and generally keeping the site updated and fresh. More major changes to pages, or the insertion of new pages or sections are charged for on an ad-hoc basis.
I share your view that a business web site should look clean and professional - no animated gizmos and background music etc. and that it should be fast and easily navigated. It is showcasing the business to the world after all, and nothing damages a company's image more than a badly designed and constructed site.
FrontPage is being used more and more nowadays, and a well-built FP site is as fast as any other. Dreamweaver is probably more versatile, and there are other good applications. Of them all, Dreamweaver probably has the steepest learning curve.
Don't hesitate to come back if you need more help.