أحسن الله اليكم is paying an entry fee for competing in permissble things allowed even tho there is no reward after the competition. The fee is just for the sake of filtering out unserious people?

If nobody wins anything from the money and the fee is only a charge for organizing and for filtering out those who are not serious, this is not the gambling the scholars forbade and there is no harm in it. If the fees are gathered and handed to the winner, then it is gambling and it is not allowed.