It varies... you can find guys on Craigslist to do it for about $25 a page, but you find pros doing it for $1500 a page.
The thing about a web site is that it's 3 things: Graphic design, Site design, and copy.
The graphic design is the general look of the site. It generally runs between $300-$3000 to get this done, but you're safe on the lower end.
Layout is the one people most often get wrong because they wind up doing it themselves. Then again, the only people who know how to do this are the SEO guys. Sure there are some reputable ones, but most sell snake oil. If you do it your self, make sure it's easy to find everything and that your page names are intelligent, and the titles reflect what's on the page. I'm assuming your clients will do this for you, so there's no need to charge. There is a good marketing oportunity to offer a design review for a little extra to make sure that the pages maximize performance.
Copy is the text on the page. If you're selling thing for manufacturers, you might be able to get away with their copy, otherwise make sure your copywriter is great. They range in price from $25 an hour to $150 an hour or so. It usually takes between 60-90 minutes per page for your standard web page.
So if you're offering these things to your clients, I would recommend that you outsource anything you're not a pro at. The quality will shine through.
Anyway, make a spreadsheet, figure out how much time you will spend and money you want to make per project, and run those numbers to see how much you need to charge. Trying to charge what the market will bear without analysis of whether it's worth it isn't a good plan,