The whole instrument cluster costs about $60 on Ebay. Its relatively easy to replace on E36 - but needs removing of steering wheel. Check DIY guides or do a search - there is a writeup with photos. You'll have a problem though - the odometer reading will not be the same as computer's. Even after reprogramming with approximate mileage, there's still an indicator of odometer tampering (somebody posted exactly where E36 keeps proper mileage settings - but I forgot). But then again, you have an E30, so I don't know anything about those.