Startup Idea : B2B SaaS with a monthly subscription model?

I have this idea in my mind for quite some time. I'm a young student studying Web Development (full stack). I am quite fluent with Laravel and Vue.This allows me to build custom CMS/SaaS Solutions super fast. My friend and I were wondering why we don't just build custom SaaS solutions for businesses. And charging a monthly fee (ex $300 - $500) for using the solution.We both don't have experiences in sales but are not afraid to go door to door of businesses asking if they need a custom SaaS solution for their business, and proving a custom demo for free that we can make in a week.If they agree to continue after the demo we charge them for the demo and let them use the system for a cheap price. While we continue making the system more feature packet each week we charge them more until we reach $300/$500.Example:We create a demo that they like, they pay $100/month for using this demo. Each week we release a new version with new features, the monthly subscription increases by $25/month until we reach around $300-$500 a month.Is this a suitable business model.I am a new entrepreneur and would love some feedback.Thanks for reading :)