You guys need to break down fixed costs (e.g. insurance) from variable/direct costs (e.g. fuel, 50hr checks, etc).
Then you will see that the business case hangs heavily on the utilisation of the asset.
In the UK, utilitisation tends to be poor - due to poor weather much of the year, poor business organisation at many schools, freelance instructors not turning up, poor aircraft condition resulting in a lot of downtime, the school being unwilling to fix each defect and instead waiting for them to accumulate, etc.
I did my IR in Arizona where the PA28-161s were flying 500-1000 hours/year. They were flying so much that the maintenance was done evenings/night, and the bowser would drive around then too. At that level of utilitisation, they could scrap those planes every year or two and still be quids in.
The variable costs can vary a lot too. If you have a uniform-type fleet and have an in-house engineering business, your maintenance is much cheaper because you are not paying somebody else's profits and also you can buy parts in bulk from the USA.