What cost are you referring to?
Policing, health service and welfare costs mainly in having to deal with gamblers turning into criminals to feed their habit (robbery, assault, burglary, manslaughter, murder, fraud...) or when they cause their family grief/lose their job/go homeless or whatever other possible outcome that can befall them/their victims.
Having a moral **** by blaming the initial gambler as many seem to enjoy doing, doesn't really do anything.
Anyway, here's a fine example, how much policing, judicial, prison service costs might he rack up just by himself?
https://www.birminghammail.co.uk/news/midlands-news/losing-gambler-rips-man-out-17586073
A gambler 'who lost all of his money' launched a vicious assault on a man in a wheelchair in a bid to steal his £10,000 winnings.
The victim had gone to the Grosvenor Casino in Broad Street and won a "substantial" amount of money consisting of £9,000 in cash and a cheque for £1,000.
During his winning spree he had been followed around the casino by Anjum Rahim as he played the tables on March 30, last year.
The victim, who used a wheelchair because of a spinal problem he had suffered years before, then left the building to have a cigarette.
He was then approached by Rahim, who told him he had lost all of his money and asked him for £20 so he could get home.
The victim gave him the money but when the defendant asked for a further £20 he refused.
Rahim then grabbed the man's jacket, pulling him from the wheelchair and they struggled on the ground, said Peter Grice, prosecuting at Birmingham Crown Court.
But the robbery bid, which was captured on CCTV, was foiled after two members of the public intervened.
The victim suffered bruising to his shoulders, back and arm.
Rahim, 39, of Somerville Road, Small Heath, who had previously admitted attempted robbery, was jailed for three years and nine months.