Like hardware maintenance, the goal of on-going software support is to optimize the continuing utilization of the system. In order for this goal to be achieved, the client needs programming support, telephone "hot line" support, technical support, all with perhaps an accounting "twist" - available from responsive and experienced computer professionals.
Every single day we get calls from long-time clients who need something customized in their system. Perhaps someone in their organization has come up with a new report they need. Or a key supplier has placed a new requirement on their company. Every day!
Every client needs customizations for their system to fit and continue to fit their unique operation. Without this on-going design and programming support, the system will eventually fail. Sure, in the short term you can make do with spreadsheets. But over time, those individual spreadsheet "fixes" will become entire "systems" in their own right, and you will be back to double entry of data.
What you need is a system that provides the tools for customization, a software provider that is staffed for this type of support and can efficiently make those customizations for you, and a software system that can be upgraded cost-effectively even though it has been customized. That's the answer, and it is completely available.