I would say that it depends on the condition of the mug and where it was made. Check on eBay. No more than £35 for a superb quality one anyway. You'd need to have a Queen Victoria one or previous...
The 1881 three cent nickel (which has exactly the same diameter as a dime - 17.9mm) is a common date for the type. The coin is worth $15-$25 in circulated condition, $40-$60 in very nice circulated...