If you have the document in an electronic format such as a Word file, then translations are generally priced according to word count and a rate per 1000 words of the original source text. The rate is established on the basis of how technical the content of the document is, along with any additional requirements you may have (for example, if you require additional proofreading).
Please note that this is not designed to be the cheapest service available anywhere on the Internet. Rather, it is designed to be a reasonably priced service for those whose main focus is the quality and accuracy of their translations. Typical rates by word count range from £60-£100 (or around $100 - $150) per 1000 words, depending on the nature and length of the document.
If the document is not in an editable electronic format (for example, if you have a scanned document held in a PDF file), then the price may be established on the basis of the page count.