Face value if circulated, up to $30 or so if crisp and unfolded.
A Series 1950 $10 bill typically sells for around $20 in circulated condition. The Series 1950A $10 bill has a lower value, usually selling for around $15 in circulated condition. The value can vary depending on factors such as condition and rarity.
Please check your bill again. "E" is the highest series letter for 1950 $20 bills. You're probably looking at the Federal Reserve District letter instead; the series letter (if any) is next to the date. When you've identified the series letter, check the question "What is the value of a 1950 [letter] US 20 dollar bill?" for more information.
1950-E is the most valuable $20 bill in the 1950 series. As of 09/2012 values are in the range $50 to $65 for a bill in circulated condition. An uncirculated one can bring $90 or more.
Current retail is $12 to $15 in circulated condition, $20 if crisp and unfolded.
Despite their age, $20 bills from the 1950 series rarely sell for more than a dollar or two above face value.
The only U.S. $20 bills with dates in that period were the 1934 and 1950 series. Most 1934 bills are worth about $22-24 in average circulated condition. Most 1950 bills are worth face value to $22. The exception is a 1950-E bill which retails for $45 to $60.
Please check your bill again. All 1950-series $20 bills were printed as Federal Reserve Notes with the familiar green seal color. The last red-seal $20 bills were dated 1914.
Right now those are only worth face value. They just aren't rare.
The E subseries had the lowest printing for 1950-series $10, $20, $50, and $100 bills. They were actually printed in the early 1960s and were soon superseded by the new 1963 series. For those denominations 1950-E bills are scarcer than 1950-dated bills with other series letters.
In Choice Crisp Uncirculated condition, it's worth about $25 if you can find an interested buyer. Any worse condition than that has no added value.
All 1950-series US $20 bills were issued as Federal Reserve Notes, so they all have green seals. Please see the Related Question for more information.
In Choice Crisp Uncirculated condition, it's worth about $25 if you can find an interested buyer. Any worse condition than that has no added value.