The only US Coins to carry a C mintmark were gold coins struck at the Charlotte Mint from 1838 to 1861. The mint mark position on a 1950 dime is on the back at the bottom of the torch:
No mint mark = Philadelphia
D = Denver
S = San Francisco
There's more information at the Related Question.
C$0.75 to C$10 depending on its condition.
The green seal indicates that your bill is a Federal Reserve Note. Please see the question "What is the value of a 1950 C US 10 dollar federal reserve note?" for more information.
There are no 1950 $1 bills. The nearest dates are 1935 and 1957. Please look again and post a new question.
To clear things up, the bill wasn't printed in Philadelphia. That's the Federal Reserve District that distributed the bill, but it was printed in Washington. Please see the question "What is the value of a 1950 US 100 dollar bill?" for more information.
Please see the attached link.
There were many different denominations of bills with that date and series letter. Please post a new, separate question with the bill's denomination.
Please check your bill again. There are 1950 A and 1950 C $10 bills but they're different. The series letter is next to the date; any other letter isn't a series letter. Neither one is rare, though. As of 03/2012 they would retail for $12 to $15 in averaged condition.
Please check your bill again, including the banner across the top. A blue seal would indicate that it's a silver certificate, but no $10 silver certificates were dated 1950.
On average $6-$10 depending on condition. http://www.pcgs.com/prices/PriceGuideDetail.aspx?MS=1&PR=1&c=703&title=Mercury+Dime
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?"
1950-series $10 bills were only issued as Federal Reserve Notes with green seals. Please check your bill again and post a new question with details that would help to better ID it.
Despite their age, $20 bills from the 1950 series rarely sell for more than a dollar or two above face value.