The short answer
At 100 units most US property management software lands between $100 and $450 per month before fees. Yardi Breeze is the cheapest published price at $100 per month. Rent Manager and Propertyware sit on monthly minimums of $200 to $450, AppFolio Core is reported near a $298 minimum, and Buildium Essential reaches about $297 once every tenant pays one online rent payment.
Letting costs $189 per month at 100 units and stays at $189 all the way to 150, so the next 50 doors you take on do not change the bill. It does not process rent payments, screen tenants or list vacancies. Tenants keep paying into your bank account and Letting reads the bank export.