VoIP Vs TDM Telephony

Hi all, i have a dificult customer and im trying to convince to use VoIP isntead of old TDM telephony, he dont want VoIP because the handset are very expensive than traditional handset, but i dont know of convince him and explain the advantages of VoIP, this customer is a BIG new hotel and they dont have nothing deployed at this time, can somebody give a hint?….