That really depends on the quality of the model and what people want to pay for it (which differs from person to person and what the model can be used for). If your model is of proffesional quality with e.g. many animations and high quality textures etc. you can try to ask some money for it. If you are unsure about the quality of your models, try comparing it with models from proffesional sites like
http://3dmodels-textures.com/ . There you can also find prices.