While I have to admit we may be lucky to hit 100k (though I'm not sure it's TOO unreasonable), sub-10k seems to be the territory of obscure, unhyped portable games from the likes of Aksys, Xseed, or (before they got more selective) Atlus. Unless damn near everyone pirated/imported with no plans to buy the US version I figure at worst total lifetime sales would be 30k or something.
30k? I think that's way too generous. The game will receive no actual marketing and is going to have to rely solely on critical support and word of mouth.