Appointment reminder

There are so many appointment or even crm app out there, but the pricing is high for the main pain point - which is to send sms/whatssap reminder to reduce the rate of no-show. I plan to build a small reminder saas with a 10$ per month or less to show this problem, the UI should be simple, create event, insert phone, set when to to send the sms before the appointment.

I think this is a good solution for small business like dental, property agent etc coz I found the current solution is too expensive (but again the challenge on my side is how to market it and make profit because the per user accusation is high when the profile is low)