This is a fair question for clients and prospective clients to ask. Unlike many areas of the law, the more unique the trademark as relates to the goods and services, the less costly the trademark is likely to be. The reason for this is that a unique mark will more likely sail through the USPTO than will one that is more descriptive. For example, Sludge, as a trademark for salad dressing would likely be approved quickly, whereas Salad Sauce would likely run into problems.
The fewer the goods or services associated with the trademark, the less the filing fees will be. The filing fee for each class of goods is $325 (unless you can use one of the canned descriptions, which can reduce the cost to $275).
Searching a trademark can cost between $100 and $500 or more, depending on the type of search requested or needed. A basic search of USPTO records, and the Internet, using a number of search engines is typically in the $200 range. Depending on the results of the search, further information may be necessary.
Legal fees for filing a trademark application, including the basic search, typically run about $500.
There are two kinds of applications. The first is based on actual use. This requires prior use in commerce and examples to be filed with the application. Advertisements, web pages, photos of the product for sale are some of the kinds of examples I have used. Many trademark applications are filed on the basis of intent to use, that is for a product or service yet to be offered in commerce. These types of applications require an additional filing fee (currently $100 per class) when filing an affidavit to allege use.
An unknown cost is the time required to respond to office actions from the Trademark Office examining attorney. Simple issues may be resolved for a few hundred dollars or less, more complicated issues can cost considerably more. Again, choosing a unique trademark and an appropriate description of the goods or services can minimize (or even eliminate) these costs.
The bottom line is that an application for a unique trademark, for a single class, already being used in connection with the goods or services, will probably run about $800. The typical case where an office action has to be dealt with, or an application to allege use has to be filed, will probably run to between $1200 and $1500.
As always, I am happy to respond to questions.