if you feel a player gets bored playing your game for 80 hours don't you think you'll get bored making a game that long? which will take you 30x as long as the game is in length?
Nobodies trying to hold back your grandiose ideas. but imagine this for a second. if you were planning to start creating music, would you make a short 4 minute piece or a 3 hour orchestral piece?
don't get carried away by ambition. it's good to have, but use it to your advantage making something that a little more, completable.
depending on the quality and look of the game, and knowing that no one really has made a 80 hour 2d game, id say you could charge 10$. i know i probably wouldn't pay more unless something REALLY blew me away.