I'm not a native speaker and I have always heard that "sale" is pronounced "sail/say+l", and "sell" is pronounced "cell". But my teacher who is a lawyer always pronounces "sale" as "sell". He is not a native English speaker either but his grammar and vocabulary is very good and he really puts effort into making sure that whatever he speaks, he says it correctly.
He even spells it out when we're confused, saying "it's SELL. S-A-L-E - SELL."