What @[email protected] said below, but instead I’d recommend You Need A Budget (YNAB). YNAB is amazing, and despite not liking paying for subscription services, I keep using it and not getting firefly (and I do self host my own things). It’s like $100 a year and will save you far more than that if you use it correctly. Check them out: http://www.youneedabudget.com
Make sure to read their intro stuff on why they recommend doing things the way they do, as active budgeting isn’t for everyone.
Shhhh you just described iterative development. Careful not to be pro agile, or the developers with no social skills will start attacking you for being a scrum master in disguise!