mice are cheap but you seem to only present the bits that support your point of view
"Among these rodents, the majority of genetic studies, especially those involving disease, have employed mice, not only because their genomes are so similar to that of humans, but also because of their availability, ease of handling, high reproductive rates, and relatively low cost of use"
http://www.nature.com/scitable/topicpage/the-use-of-animal-models-in-studying-855
genetic similarity in mice is a big factor, if mice didn't have it they would pick another cheap animal that did.
(20min delay)