Odoo Community even though is open source and available for everyone to install, there are associated costs for running it such as:
- Server
- Maintenance
- Upgrade
Some of them overlap if you decide to have Odoo Enterprise on your own server, however, with enterprise, it is easier to keep the system up to date with the newest version and some of the additional features there can be a big plus.
In the end not always open source means a better option for your budget, before going further with the project evaluate the needs of your company and what would best match them.
A more in-depth overview of both versions is available here.