"Me gustarían tres (sin tilde porque es un monosílabo) sangrías".

Usually you would only say "me gustarían trés sangríaS". or in English.. "I'd like three sangrias" If you are the one who will drink all three of them ! You would most likely ask for a jug though :P "me gustaría una/media jarra de sangría". Anyway, If you are not gonna drink them all "trés sangrías por favor" would be more native-like. Note:You would only Not add an "s" at the end of a plural if you asked something by it's brand (sometimes).

me gustarían 3 sangrías. Debes recordar la norma de la pluraridad.