Well this is the game being played. If you run a business you don't want customers like me who seek value and privacy. You'll make a lot more money from those with plenty of disposable cash who don't mind adding yet another $10/m SaaS to their monthly expenses.

I thought about creating a budget SaaS but what puts me off is

(i) Your target money is in a budgeting mindframe and so yeah they are going to be looking for the cheapest option.

(ii) There are so many budget apps and they are good and fairly cheap.

YNAB4 is the best as far as I am concerned, unless you need full double-entry accounting. The user interface is superb. It is going to be hard to come close. My ideal budget app is YNAB4 but with some of the opinionated envelope-based budgeting calculations being more flexible for those who do have some cashflow buffer.

I'd literally keep a Windows 10 VM for the next 20 years to run it :-) unless something with a better UI comes out which I doubt.