If your anemone is one that eats fish (Ritteri, Haddoni, etc) then you can feed it thawed silversides. A cheaper food source is to go to a bait shop and buy a box of frozen anchovies or sardines. I feed my Ritteri a frozen (thawed) sardine every couple of weeks. Of course, much of this food will be expelled as waste, so be advised.
HTH
James Wiseman
HTH
James Wiseman