Unexpected Ticket Costs

Imagine your favorite sports team is playing at a nearby stadium, but you delayed purchasing a ticket until the last moment. You have the option to buy a second-hand ticket for $50, but there's a 20% risk it might be invalid. Should the ticket fail, you'll need to purchase an official ticket at the stadium for $70. What is the expected cost of attending the game? How much money should you budget for this event?