At the very least, it fills the empty space you got with your Internet service. Costs are similar to creating a nice professional 4-color brochure of similar scale. Don't think you can just put up your brochure though, the mechanics are way different. At best the designer can cut some graphics and copy some text from your brochure. There will be forms to place orders, request quotes, etc.
Production costs are similar to a color catalog of similar scale.
This kind of site can be nearly as good a sales tool as an e-commerce site, since most people still pick up the phone to actually place orders. You can't negotiate by filling out a form, after all, and a sales person may know about conditions, new products or price changes that aren't posted on the Web yet. Many people feel their credit card information is more secure that way, too, and given how easily most e-commerce sites are hacked, they're probably right. Cost varies in the extreme depending on who is doing the work and how that work is being accounted for. If it can be done as part of normal operations, so much the better.