What is the value of a twenty dollar bill 1977?

You have $20. You need to go back about 50-60 years before most bank notes (of any denomination) will start to accrue added value. At older ages, the condition of the note will be important...put the 1977 $20 under glass today and you might have, say, $30 or $35 in 30 years--about enough to cover a frame for the bill at today's prices.