Rent Manager here - it greatly depends on what you would like to use the software for as well as how you would like to use the software. Both are based on a double-entry accounting system following GAAP principles, a work-order management system, and property management tools with reporting.
With Rent Manager Online, we store and backup your data regularly, support is included, and you are also open to use some of the online capabilities we have such as Web Portal Suite (online management tools for residents and owners including online payments), marketing automation and integration, report automation, and more. This starts at $75 per month per concurrent user (how many people need to be in the system at the same time).
With Standalone, you purchase the program outright - you will be responsible for storing and maintaining your own data. Support is included for the first year with Enterprise Unlimited, then there is an annual maintenance and support fee starting the second year. Support is included with Enterprise-per-Unit for the first 30 days only. A sales representative can go over the Standalone pricing with you specific to your setup.
If you need any other clarification, feel free to let me know or give us a call!