[GaGlets(R)]

i dont suggest you to use GetTickCount because if your server will run 24 days without restart or smth then it will fu** your server up.

Use a repeated timer for a player.

pawn Код:

OnPlayerEnterVehicle
If(GetPlayerVehicleID(playerid,yourcarids))
SetTimerEx("Fuction",1000,1,"i",playerid);

forward Function(playerid);
public Function(playerid)
{
      GivePlayerMoney(playerid,-yourcash);
      //messages and other stuff
}

Edit:

Oops use Callback OnPlayerStateChange.
if(newstate == PLAYER_STATE_PASSENGER)
settimer...