The only way to buy Dreamweaver is as part of a Creative Cloud subscription direct from Adobe, for which you pay monthly or annually. There are two broad options. The first, and cheapest, is to subscribe to Dreamweaver only. The second is take out an All Apps subscription. The latter will cost you more, but gives you access to all of the Creative Cloud apps, along with other benefits.
If this cost seems too high, bear in mind that Adobe often runs special promotions; we track the best in our guide to Creative Cloud discounts. There are also discounts for students and teachers (see below), as well as separate pricing for businesses, schools and universities.