The closest railway station to Malcesine is Rovereto (33 km / 21 miles). The single train fare is €6.95 if you use the Regionale trains (with journey times of around one hour). Eurocity services (taking 37 minutes) cost €9.90. Frecciargento trains also take 37 minutes but the fare is €13.00. (All services are direct, with no changes involved).
A TripAdvisor thread from three years ago quotes the taxi fares from Rovereto as €1.50 per km, so that would suggest a fare of around €50 to Malcesine (but it would probably be better to allow at least €60 to take inflation into account).