I'm afraid you have been given slightly insufficient information. 50e notes with a serial number starting with L are not particularly rare. Some 372889 of them have been registered to EBT, of which 1707 by me.
Pay close attention to the six-digit printer code on the front. D001 ones were also very common back in the day, because those were printed by Setec. Setec has not printed any notes for a decade or so. Those might already have
some value if they are in good condition, because they are getting rare. The last time I saw one was about a year ago. About the same goes for H006.
However, if you have a note with a printer code starting with H005 or H007, or something else not mentioned here, you may have a more valuable note in your hands, perhaps around 10x.
Disclaimer: I'm not collecting or buying/selling banknotes, there are better experts in here than me
