The bank’s original estimate of costs in August last year put costs at £98 million excluding VAT.
Sources close to the defence said the bill was in line with its expectations because of the delays to the trial, which was originally due to start in December.
An RBS spokesman said: “We continue to strongly contest these claims.”
Typically, winners are awarded around 70% of their costs, which would be covered by the claimants’ legal insurance. RBS will face a much bigger bill if it loses.