At the time, it was worth one dollar.
its a $5 bill, its worth $5
In circulated condition, it's still worth one dollar.
If a dollar bill were printed in 1977, it would be worth $1.00 right now (in 2008). If a $20 bill were printed in 1977, it would be worth $20.00 right now (in 2008). A candy bar that may have cost $0.05 in 1977 would cost around $0.75 now. But then, a candy bar isn't a dollar.
Realistically, it's still worth one dollar.
Face value only.
It's probably a regular series 1977 dollar bill with an Elvis sticker covering Washington. As currency, it's only worth one dollar. To a collector, it's worth as much as someone is willing to pay.
10 dollars
$50.00
It's still worth one dollar, maybe two to a collector if it's in mint condition.
20 Nickels
Five dollars, save it though in the future it will actually be worth something.