[BroZeus]

PHP код:

public OnPlayerStateChange(playerid, newstate, oldstate)
{
      if(newstate == PLAYER_STATE_DRIVER)
         if(GetVehicleModel(GetPlayerVehicleID(playerid)) == 520 && GetPlayerScore(playerid) < 500)
               RemovePlayerFromVehicle(playerid);
     return 1;
} 


This code will remove player from Hydra if his score is less than 500.
520 is Hydra vehicle Model ID, refer to https://sampwiki.blast.hk/wiki/Vehicle_Model_ID_List for list of vehicle and their model ids.

EDIT: Too late answer has been already posted above.