Or would apple cider mixed with some (how much?) apple cider vinegar or lemon juice be better?

Any white or light fruit juice or lightly fermented fruit alcohol (white wine, white grape juice, or perry - pear cider).
If all you have is an acid like lemon juice or vinegar, yes ok to use but I would only use it to replace half the wine. And use water for the other half.
Otherwise the overall dish might be very sour.