I've done three websites so far.
www.geocities.com/cremerabbits was my first (meat/show rabbits),
www.freewebs.com/cremerabbits (pet/fiber rabbits) was done about six months ago and I created
www.purequackery.com last month for the family farm. Also have a "blog" connected with my rabbit websites:
www.verdantrabbitry.blogspot.com.
I think a good website should include much of the same information you'd put in a brochure, but expanded on. You have a lot more space on a website, so you can put in lots of photos and much more detailed information than you'd normally be able to include in promotional materials. My sites all include basic information about the business and detailed information about what's being sold. It usually also includes articles related to what you sell to draw a wider audience than the people who'd be coming just to buy things. (ex: Since I sell rabbits, I have articles on how to care for rabbits and information on breeding them.)
My oldest website has been up for about two years.
We spend a total of about $12 a month for web space for purequackery.com plus an additional $7 annually for use of the "domain name" (website address). It's already getting a lot of traffic, but a smaller site shouldn't cost you more than $5 a month or so. The other two are "free" (pop-up ads).
The book Webpages for Dummies is a great introduction to building websites - it's in plain English and it covers just about everything. I also attended a [free] workshop on e-commerce at a community college and gleaned a lot of ideas just from surfing. Your local library should have several books on the subject, but if the book was published more than 5 or 6 years ago, I really don't think it would be worth your time.
I try to update things at least once a month and ideally I post a new entry in the blog every couple of days. The home page on my rabbit websites and the sales list gets updated more frequently.