White background colour of image changes to transparent or different colour

Hi, I need someone to change the background colour of images from white to either transparent or add a new colour/layer. I am reasonably skilled in PS, but this one is proving challenging. I have over 1500 images that the above needs to be done. I need the cost to be low so therefore clipping paths are not an option. I have tried to add a layer and change the layer to either multiply or darken. The result is almost there. However I must make sure that any whites are not changed. I am happy to pay a small fee to anyone that has the answer to removing/changing the background(white) to another colour using a blending mode but without effecting the whites of the products. Is there a way to make the selection f the blending less or more tolerant? I look forward to any help. Dominic