Then there are the added capital costs of building and maintaining prisons. To give one recent example, the proposed expansion to Waikeria Prison is forecast to cost $1 billion.
Perhaps more importantly though, there are the inter-generational health and social costs of having a system that doesn't work.
It is a common misconception that prison deters crime and that the best approach to offending is to "lock them up and throw away the key". Lobby groups such as the highly un-sensible Sensible Sentencing Trust appeal to that sentiment.
Thankfully, current sentencing laws don't make this possible (much to the relief of the New Zealand taxpayer). Inevitably, prisoners are released back into the community.
However, in addition to the costs of incarceration, further avoidable social and health costs occur after release. Convicted criminals have the stigma of a criminal record, potential media attention around their offending and a gap in their employment history.
Although the Government spent $181 million on prisoner reintegration in 2017, it is unsurprising that, after 12 months of release, 31.2 per cent were back in prison.
We can't stop crime, but we can change the way we punish it.
Two thirds of prisoners have addiction issues which remain untreated in prison. Rehabilitation programmes in prison don't work because they are not transferable to a community setting. Prisoners are released with $350 from Winz, no job, no home, no transferable life skills and nowhere safe to go. It doesn't take a rocket scientist to work out what is likely to happen next.
If we want to make our communities safer, we need to give offenders the tools they need to stop the cycle of crime.
Compare the cost of all this to the cost of keeping one person on electronic monitoring for one year - around $40,000.
Home detention is no walk in the park. You are confined to the perimeters of your property 24/7. As your sentence progresses, you may earn the right to attend drug and alcohol counselling for a couple of hours a week or to go to the gym for two hours a week.
Besides that, you are confined to the four walls of your home. Towards the end of your sentence, you may be allowed four hours of social leave a fortnight. Some electronic monitoring has the capability to alert probation if drugs (including alcohol) are being consumed. Your every move is monitored by a GPS tracker.
Another benefit of this type of sentencing is that the offender is able to work, if he or she is lucky enough to find a supervisor to vouch for him. This means actual reparation can be made to victims, as opposed to $2 per week from a prisoner. Community sentences have the benefit of allowing an offender to stay within society whilst ensuring the public are kept safe, at a fraction of the price.
To deter crime, people need tools that enable them to reconnect with society. Downsizing prisons will free up money to be redirected to where it will help reduce the continuing cost of people who have been damaged and marginalised by the prison system. Remember, one third are back in prison within 12 months of release.
Addiction causes crime, and the opposite of addiction is connection. Offenders need to be reconnected to society with jobs, social inclusion, positive relationships and help with the issues that caused them to offend in the first place.
Decreasing the prison population will not increase crime or risk to public safety. It is time to stop the nonsense, end the war on drugs and create evidence-based policies. Rather than more prisons and prisoners, increased management of electronically monitored offenders could help reduce recidivism. An extension of clean slate legislation could remove the stigma which can prevent an offender's economic reconnection.
You wouldn't buy a billion dollar house if it was eventually going to fall off a cliff, so why are we willing to make an investment that we know is going to fail?
• Julia Fyers has a masters degree in law and is a legal researcher working on issues of human rights and drug and prison policy reform.
