Depending on the type and number of windows you have, washing them yourself can turn into a multi-day project. Professional window-washing services will usually clean the windows (inside and out), screens, and sills as part of the basic package.
Some will move furnishings and protect floors and surrounding surfaces at no extra charge. The total cost will be based on your location, the number of windows, and any extras like blinds or storm windows that you also want cleaned.
Call several services to compare what they offer. Most will provide free estimates for your consideration. Check the websites of associations like the International Window Cleaning Association to locate certified members in your area.