SetTimer("timer", 3000, 1); // create a repeating timer of x (here 3000) milliseconds
new allowhydra = 0; // creating a variable which will be used as a boolean to check if he/she can use a hydra

// next, we are going to create the timer
public timer() {
// check if his score is lower than 200
if(GetPlayerScore(playerid) < 200)
// score is lower than 200, player cannot use hydra
  allowhydra = 0;
else
// score is higher than or the same as 200, player can use hydra
  allowhydra = 1;
return 1;
}

OnPlayerStateChange(playerid, new_state, old_state) // I may have this function wrong, please check the manual that corresponds to this function
{
  // checking if the player is entering the vehicle as a driver
  if(new_state == PLAYER_STATE_DRIVER)
  {
    // check if the vehicle is the hydra where he/she cannot enter when points are below 200
    if(GetPlayerVehicleID(playerid) == THE_HYDRA) { // whereas THE_HYDRA is your vehicle ID of the hydra
      if(allowhydra ==0) { // checking if the player has a score below 200
        RemovePlayerFromVehicle(playerid, GetPlayerVehicleID(playerid); // remove the player from the hydra
        SendClientMessage(playerid, COLOR_YOURCOLOR, "You are not allowed to fly the hydra");// Send the message that says that he/she is not allowed to enter the hydra
      }
    }
  }
}