This falls into the not a trivial question category. :) You will have to specify the material, the resolution (tolerance) you want the model printed at, how big it is, and how much material is required. This will determine what type of printer is used and how long it will take, which are going to be prime factors in the cost. Also be aware that some models print better on certain printers. My advice is to look on shapeways for something similar to what you are printing and that should at least give you a rough guess. If you already have a model, I think that you can upload the model and get a quick quote on it. Best of luck!