Omega 2.5 V6 cam belt change

You don't mention the year, and according to Autodata there are also subtle differences depending on which of two tensioner pulleys are fitted, but assuming an Omega "B" MY '97-00, engine code X25XE, the change interval is every 4 years/40K miles. The tensioner pulley must also be replaced. The time given is 2.4 hours, so it's not going to be particularly cheap.

Whether it's worth buying knowing it needs a cambelt replacement can only be answered by yourself; there are too many variables, such as what else might need doing, how much will you pay for the car, how much you want one etc.

Chris