I am no great expert on these pistols, but that value is ~30%-40% higher than what I've seen for .25ACP (6.35mm) examples in roughly equivalent condition.
I've spoken to a fellow at a LGS who's quite knowledgeable about older European autos. He told me that Mauser 1910s don't usually fetch more than ~$300 unless they (a) have military proofs, (b) are one of the relatively rare early models, and/or (c) have 90%+ finish. This pistol looks like none of the above to me. These guns generally seem to have thin and fragile bluing, so examples with more than ~80% are rare; most guns that have been carried and/or stored carelessly have no more than 70% finish, like this one.