The vast majority of people will find it barely comprehensible that it costs £55,000 a year to house one prisoner in a jail in Northern Ireland. This figure, which was released to Jim Wells MLA after he put down an Assembly question, is equivalent to £150 a day - a sum which would pay for a night's lodging in all but Northern Ireland's ritziest hotels.
The overall cost of keeping prisoners behind bars was £69m in 2018-19, which was down slightly from £73m in 2016-17.
Even though Justice Minister Naomi Long said that the cost per prisoner here in 2019-20 was expected to fall by almost £11,000, this figure is well above those of England and Wales (£43,000) and Scotland (£40,000).
The fact that the individual prisoner costs can be reduced here by 20% in just one financial year suggests that the £55,000 figure contained considerable padding, and this reduction may hold out hopes for the future.
The hard reality is that imprisoning people is always going to be an expensive business.
If incarceration is to be about anything more than denying prisoners their liberty, and also about education and rehabilitation for example, then that will come at a cost which people will have to judge in its overall context.
Clearly, public safety is another key aspect of penal policy. Society requires ongoing protection from a certain class of violent criminal, and it would seem an eminently sensible way of spending tax revenues to provide this.
While this is understood, as well as the question of who deserves to be in prison, there is also a clear corollary question - namely who are the people who should not be in our prisons?
A disproportionate number of young female prisoners are in jail for non-payment of fines for not having a TV licence.
The Government's mooted scrapping of this outdated practice would be a welcome boon to the Prison Service budget - and hence the taxpayer - while also satisfying the wider principles of justice.
The whole question of justice is itself complex, not only in terms of financing those who are sent to prison, but also in determining legally that our justice system is transparent and is fair.
The BBC licence is coming under scrutiny, but it does seem that imprisonment for non-payment is unduly harsh. There must be a better way to handle this situation.