Australia's fixation with asylum seekers arriving by boat has cost taxpayers nearly $2.4b since 2000, according to Budget and ANAO documents. The expenditure includes spending to deter, process and most of all detain asylum seekers who have arrived by boat. Mandatory detention of asylum seekers was first introduced by the Keating Government and continued and expanded under the Howard Government, with a proliferation of offshore detention sites designed to punish asylum seekers and deter others from coming. The $2.4 billion cost is separate from spending on detention facilities for other detainees such as asylum seekers who arrive by air, or visa overstayers -- most years, the latter exceed maritime arrivals by a factor of ten or more. The cost also does not include hundreds of millions spent on border security measures adopted under the Howard Government, nor the cost of conducting and carrying out the recommendations of the Comrie and Palmer Reports into the treatment of Cornelia Rau and Vivian Solon by the Immigration Department. The cost of establishing and maintaining facilities on Nauru, where asylum seekers were detained before inevitably being allowed to live in Australia, still remains a mystery. It was kept out of the Budget papers by the Howard Government; in fact, bizarrely, the cost of the Nauru facility is a net negative in the Department of Immigration's Budget papers since 2000, with over $35m in savings booked from the operation of the facility in 2006 -- when it held two Iraqi asylum seekers -- and a cost of $10m appearing as a Budget measure the following year, for continuation of the facility. Some of the facility's original funding came from the AusAID budget. Non-government sources have since estimated the cost of the Nauru facility at $1b over five years; a far higher figure than that offered by an Immigration spokesman in 2006, who provided a "preliminary estimate" that the facility cost around $1 million a month regardless of whether there were any inmates. The Coalition has consistently refused to provide a costing for its current proposal to reopen Nauru as a holding centre for asylum seekers. A plausible costing for the operation of the Nauru facility pushes the cost of the policy to over $2.5 billion. Also problematic is the cost of the construction of the upgraded detention facility on Christmas Island, one of the many expensive bungles investigated by the Howard Government that received critical reports by the Auditor-General. The cost of the facility has an uncertain existence in the Immigration Budget papers, appearing only fleetingly from year to year. That's because the construction of the facility was primarily overseen by the Department of Finance, with funding also going via the then-Department Transport and Regional Services. The project was originally costed at just under $200m but, according to the ANAO, ended up costing $317m due to poor management by the Department of Finance. Another $200m has been spent in the last two years to further increase accommodation on Christmas Island and provide other detention facilities. The cost of detaining asylum seekers only -- that is, removing costs for deterrence and anti-people smuggling activities -- totals just over $2b since 2000. During that period, just over 18,000 people have arrived by boat. That means taxpayers have spent about $113,000 simply to detain each asylum seeker, on average, across the period. Our obsession with detention comes with with a big price tag.