Just go for it in your favorite programming language, it's a nice exercise and in the meantime you can learn about (double entry) bookkeeping.

I did that for myself and it took me at most three months of parttime working on it, resulting in a bespoke solution. No need to keep paying some SaaS or fiddling around in Excel. One still needs to learn the bookkeeping system though, but that's true for all options. A SaaS is not magically make that go away.