The price will vary depending on your individual needs. If you just need a brochure type web site, it can cost as little as a few hundred dollars. A one page web site can cost about a hundred dollars. The more you want on your web site, or the more you want visitors to be able to do, the more it will cost. Don’t forget to include hosting and a domain in your budget.
Ecommerce (selling products) can be a bit more expensive and can cost up to a couple thousand dollars, depending on how many products are in your shopping cart, what payment methods are accepted and how easy or hard they are to implement, among other factors.