Identify suitable stock photos

We have developed a homepage with some pictures/fotos. We have identified suitable fotos, mainly from istockfoto. However, the pictures we selected are quite expensive. Your job is to find suitable alternatives with all legal rights that are similar, but cheaper. You receive a list of fotos (hospital environment). You show me alternative pictures with similar motives. I agree that the picture is comparable or better. You tell me where I can buy the picture for a cheaper price than our benchmark. Must be a clear legal situation, we need the certified right to publish the picture on our webpage. You need a good overview of stock foto dealers. Or even better, you have a large amount of credits and are allowed to resell suitable fotos at a good price.