Leah,
$500 sounds good to me, but I wouldn't tie it to the actual number, in case they come back and say," we're only printing 2,500. Get some legal language from the internet about 1 time usage, payment etc. And as mentioned above, your artist info on the back is mandatory for "small" jobs as this.
I might also talk to the printer and order some cards yourself, possibly without the Corporation info on them, which you can buy very cheaply at this volume and use for your own marketing purposes.
Rich