I need to buy a particular brand and model of stepper motor and I have found the product on the manufacturer's web catalog, but with no price listed.
In industry, an equipment manufacturer hardly ever sells directly to the end user. They supply distributors in bulk at a negotiated price for each shipment of however many units the distributor orders. The price-per-unit varies accordingly, so there's no point in listing it the way you would for retail products.
If you only need a single unit of a product, generally the manufacturer is not going to want to do business with you. They produce many units at a time, as required to supply their distributor(s), in order to use their facilities and personnel efficiently.
What you need to do is find a distributor or wholesaler who carries that manufacturer's products and is willing to sell directly to you (retail business). Grainger is one example of a company that does this, though you may have to work for a company that has a business account with them in order to just walk in and order a single item.
You can usually find the contact information for a local or regional distributor on the company's web site or in their catalog, provided they do business in your area. Sometimes, especially when dealing with a foreign supplier, they won't have an existing business relationship with anyone in your region, and then you may need to look for an alternative product or work with a foreign distributor as well, which can be a real headache for just one piece of equipment.