I was just given a bike for free what can I expect

My grandfather gave me a 1980 Honda CX500 as a college graduation gift. He bought it new off the floor and rode it for 2 seasons to drive to work then put it in the garage for about 20 years until I was about 6 when he would get it out and take all the grandkids on a ride once a summer. It has not been started in about 10 to 15 years but was covered up in a garage the whole time. He is not positive if he drained it of fluids before putting it away but said there should be absolutely nothing wrong with the bike to his knowledge (except the leather seat) what type of repairs should I be expecting for this bike and what would the cost be. As I said I’m fresh out of college so I don’t have a ton of money to blow but really want to get an idea of what kinda cost I am looking at here via /r/motorcycles https://www.reddit.com/r/motorcycles/comments/gezuso/i_was_just_given_a_bike_for_free_what_can_i_expect/?utm_source=ifttt