Doing something without being asked to do so and outside the terms of your employment is called 'volunteering'. Volunteers don't get paid.
Transitioning your workplace to an unauthorized homegrown system without being directed to do so and then refusing to provide said workplace with access to the program source unless you receive some sort of payment is at best unethical and at worst extortion.
Look, you told work they could use this thing. They said they have no budget for it. You did it anyway. Thy still do not have any budget for it. You can either deploy your thing, start using it, make your work easier for yourself and your colleagues, and accept only the 'payment' of knowing you have done good work for a cash strapped organization, or you can throw your unrequested work away and do your job according to the terms of your employer - even though their way is harder and less efficient.
Seriously, they have no budget for this. They have told you they have no budget for this. Be a volunteer or don't be a volunteer, but don't be an extortionist.