As of 01/2009 auction prices for a circulated 1934-C $50 bill are face value to $70 depending on how worn it is.
Despite their age, most series-1934 $50 bills are not scarce. $50 was a considerable amount of money then so (relatively) high-denomination bills didn't see a lot of circulation.
A denomination is needed. Please determine your bill's denomination and look for the question "What is the value of a 1934 C US [denomination] dollar bill?"
Value of 1934c $20 bill
Please check your bill again. No 1934 C $1000 bills were put into circulation. You may be referring to the Federal Reserve District letter; the series letter is next to the date. There's more information at the question "What is the value of a 1934 US 1000 dollar bill?".
If worn, about $22. If it's in better shape, it could retail for up to $28.
As of 04/2013: 1934: $625.-$1300. circulated, $1500+ uncirculated. 1934-A: $610.-$1200. circulated, $1400+ uncirculated. 1934-B, 1934-C: None released to circulation.
Please check your bill again. All HAWAII-overprint bills had brown seals rather than red, and "A" was the highest series letter used on $20 bills. There's more information at the question "What is the value of a 1934 US 20 dollar bill with HAWAII on it?".
what is the value of a $5.00 silver certificate with dates 1934 D and 1934 C worth in good shape
As of 01/2009 auction prices for a circulated 1934-C $50 bill are face value to $70 depending on how worn it is. Despite their age, most series-1934 $50 bills are not scarce. $50 was a considerable amount of money then so (relatively) high-denomination bills didn't see a lot of circulation.
Auction prices as of 02/2009: With a green seal, $12.-$20. depending on how worn it is. With a blue seal, $20.-$60.
Please don't assume that every old bill is a silver certificate. As the bill's green seal and banner across its front indicate, it's a Federal Reserve Note. There's more information at the question "What is the value of a 1934 US 500 dollar bill?".
To explain how US bills work, they don't have mint marks because the Mint only makes coins. Bills are printed by the Bureau of Engraving and Printing. If the "C" is next to the date it's called the series letter. On a 1934 bill it indicates how many different Treasury Secretaries or US Treasurers took office since the start of that particular printing series.Please see the question "What is the value of a 1934 C US 10 dollar bill?" for more information.
Despite its age this is not considered to be a rare bill in circulated condition. As of 04/2012 values range from face to $140 depending on condition. A nice uncirculated one can bring $175-$200.