How much would a Civil War bond be worth now, if it was issued by the Union?

If someone found a bunch of 10-40 Civil War Bonds, how much would they be worth.

A 10-40 bond matures after 40 years (but redeemable in 10) at around a 6 percent interest rate. So if I found one issued by the Union in 1862 that was worth $100, what would it be worth today?

As we all know Confederate bonds are worth nothing at all, except to collectors. However the South (Confederate) was fighting the North (Union) and both sides issued war bonds.

I am asking what a Union bond (issued in say Maine or another Northern state) would be worth. Not a Confederate bond.