$1000 per mouse? Seems really expensive.
By the way, you can poke around some of the animal vendor's sites. They mostly have their pricing on their websites along with a bunch of other information. Four really big ones are Taconic, Jackson Labs, Envigo, and Charles River.
Source: https://xkcd.com/980/huge/#x=-1166&y=-2798&z=5
Add to that expenses for the experiment, and $1000 seems not far fetched.
While labs have huge economies of scale—-I worked somewhere with a quarter million mice—-the mice aren’t just random field mice. Some of the genetically engineered ones are hundreds of dollars a pair (and possibly more if custom, raised under unusual conditions, etc). Xenografts need skilled labor and very clean conditions for the immunocompromised mice. $1000 seems a little high, but not much, especially if the work isn’t being done by an underpaid grad student.