For small apps I think the new announced Free Edition will cover your needs. I think Mendix will provide more info soon.
This can be found about the free edition: https://www.mendix.com/blog/a-3-step-leap-into-your-digital-future-highlights-from-mendix-world/
Here is one last piece of really great news: I am pleased to announce the launch of the Mendix Free Edition. Now, anyone can use Studio and/or Studio Pro to build whatever apps they want. Unlimited apps, unlimited users. Whether you’re a business analyst or developer, a CEO or a systems architect — go make it! You get the full power of Mendix no-code, low-code to use as long as you want to make as many applications as you want. Our goal is to enable makers to unleash their brilliance with Mendix, quickly and easily.
you can use mendix runtime on the server, however the service will stop within 2 hours (if i can remember correctly).
for using internally, you can run cron tab to restart service every 1 hour, however when you are happy with a result, please make an order ^^
Hope that help.