Q: Are you able to tell me the cheapest way to come from Gatwich to Holborn station. We are 8 persons.

A: I assume you mean by train. The cheapest way to get from Gatwick airport to central London is probably via any train except the Gatwick Express. Though the Gatwick Express is probably the fastest, its also the most expensive.

When you arrive at Gatwick airport, head for “Trains”. Once there, go to the ticket office and tell them you want a normal ticket (ie. not Gatwick Express) to either London Bridge or Victoria. They might even sell you an all inclusive ticket – for both travel to central London and also travel on the London Underground. Otherwise, just buy your underground ticket once you get into central London.
When you arrive at your central London station, catch the underground / tube to Holborn station.