Well, you say that you're intending to pay a Captain $15,000 a F/O and F/E $7,000 each (I assume it's monthly wages), doing a simple math (not counting with social contributions, pension, etc) you get, per year per each set of crew, at least:
Captain: $180,000, F/O: $84,000, F/E: $84,000, Total: $348,000
Assuming that you will have at least 5 sets of crew you get:
$348,000 x 5 = $1,740,000 per year.
Dividing this by 2,000 block hours you get $870 per hour.
All this to say that with $250 per hour for flight crew you probably will get 1 and a half sets of crew!