Buy only Thai fish sauce. My preferred brand is Tra Chang (made from only anchovy, salt, sugar), which I normally find at LAX-C. http://www.lax-c.com/
That said, I'm not sure where you get the idea you have to pay more than $4 or $5 for good quality fish sauce, as raizans mentioned above. A bottle of Tra Chang (a good hefty 24 ounces) retails for about $4.50 if I recall correctly.
Fish Sauce tks for the info . Several articles say the fish sauce from a small island phu quoc
called nuoc man in Viet Nam is very good. The internet has very interesting info under
fermented fish sauce.One article from Taiwan mentioned almost all fermented fish products
they analized had more than 50 ppm the fda limit for histamine and one had 1000ppm. This can
cause scombroid poisoning. The amines are a bi product of fermentation and are found in
most fermented products. No wonder this stuff is cheap but it does taste good.
Roughly commercial low end sauces use extracts of anchovies ect while the authentic is made from
a barrel of fermented anchovies and other small fish and lots of salt and after the fish breakdown
the liquid is drawn off and bottled. I beleive this is similar to garum which the ancient Romens
used with many of their foods