what is the value of a 1957 b silver certificate? If I was to sell it, what would I get?

At a coin dealer around only a few dollars
On eBay whatever you can get for it
1957 b silver certificate value - Google Product Search

ericblair2008 - AS per the RED BOOK ON USA CURRENCY dated 2008, the answer to your question is as follows;;
VG-20 UNC-63
# 1621. - $ 3.00 $ 9.00
# 1621*- $ 4.00 $ 15.00
THERE is a guide to paper currency at
1.9) How do you grade the condition of paper money
I hope this answers your question :: if you need more help come back to this post and post it :: Have a nice day and GOD BLESS ::
F.B.E.