As a rough estimate, I think 3x to 5x more expensive. Marmosets are smaller (smaller than squirrels) whereas macaques (rhesus/​cyno) are about 10x bigger (6 kg). And macaques take longer to develop (3 years vs. 18 months until adulthood). Finally, macaques are in high demand and low supply for pharma research.
But the benefit is that methods developed in macaques are more likely to translate to humans, due to the closer evolutionary relationship. Marmosets are a bit unusual in their embryonic development (two twin embryos share a common, fused placenta!)
As a rough estimate, I think 3x to 5x more expensive. Marmosets are smaller (smaller than squirrels) whereas macaques (rhesus/​cyno) are about 10x bigger (6 kg). And macaques take longer to develop (3 years vs. 18 months until adulthood). Finally, macaques are in high demand and low supply for pharma research.
But the benefit is that methods developed in macaques are more likely to translate to humans, due to the closer evolutionary relationship. Marmosets are a bit unusual in their embryonic development (two twin embryos share a common, fused placenta!)