2015/16, franchised TOCs only
staff: £3,170m
rolling stock: £1,606m
total operating expenditure: £10,141m
2021/22, franchised TOCs only
staff: £3,617m
rolling stock: £2,990m
total operating expenditure: £12,998m
I'm not sure if this is nominal or inflation-adjusted. Clearly, it does not include Network Rail (or any other) staff costs. And, also, it is not over the same time period as Bald Rick is quoting. There are other costs too, of course - I just provide these two as they seem most relevant to discussion.
Nevertheless, this does not seem to support the assertion that it is staff costs that is driving overall costs.