No way would it be anywhere near cost-effective to produce individual mice with each gene in the genome knocked out as the original submitter suggests. About $100,000 sounds right, and the usual rules of supply and demand follow: the only reason the arthritis mouse is $200 is because many more people need it (and because there are numerous genotypes that can induce that particular phenotype but that's neither here nor there) than, say, a random mutation in a downstream signaling protein somewhere. There's no ROI on the effort spent to isolate that gene.