Andrew,
That does not give me much to go on. It could be $700 or as much as $20,000 or more. So you are going to have to give some more info. Post a few good photos without a flash. The exposure is typically bad for detail. Start with a serial number and description of the condition of the rifle. Then a reasonable estimate can be made. There were only 160,000 Model 1886 rifles made so they are relatively rare compared to other Winchester rifles. The .45-90 is one of ten calibers which were available. There were many variations of the rifle available so they can all affect the value. #1 though is condition!!! The pictured rifle is close to $40,000.
2bit