What is the real cost of buying an IT-system?
I would say, "Buying an IT-system is like buying a horse". It's often more expensive than you thought and you can see the video on youTube how to buy a horse
You have the cost for licenses and needed infrastructure to run the software. You need installation and configuration of the new system and perhaps some custom development.
Then you need integrations to other systems and changes to existing systems. This could be really expensive.
You don't have a veterinary to call when your IT-system gets ill, but you need to have a plan B when, not if, something goes wrong.
If the new IT-system replaces an old one, you need to migrate over all information and get rid of the old one. Some people have as much trouble retiring an old IT-system as getting rid of a really old dear horse.
You also need to have a budget for daily maintenance of the system and making changes so you don't end up with a huge technical dept. If it's a new technology, you also need more education to the IT-staff.
Don't forget the business, non-IT perspective, of the IT-system. The people using the system need training and perhaps new ways of working to get the business benefits out of the system.
You may even need to change your whole business model and organisation in order to take advantage of your new IT-system.