1985 Riviera Dash Lights

My dash lights aren't working, and haven't been since I bought the car. I checked the fuses and they are all good. My interior lights all work as well, it is only the lights illuminating the speedometer etc. I think it might be the light dimmer that is also the lights switch because of how loose it feels, but I'm not entirely sure. It could be something completely different like a bad fusible link. I'm at the point where I might just take it somewhere to get it checked out, but I want to know what kind of prices I should expect first. All help is appreciated.