Free ObjecDB license for Open Source project

I'm just starting to work on small Open Source project. Currently I'm selecting suitable persistence layer. ObjectDB looks like a very good fit, but I can't justify buying license for 500$. Also we can't restrict ourselves for 10 entities :).  
So I wonder if it's possible to gain some kind of less restrictive ObjectDB license for Open Source project. 

Thank you for your answer.

I was also planning to ask something similar, so thanks for doing it.

Let's hope for a helpful answer.

If the project is not commercial you may apply for a free license by opening a support ticket and your request will be considered. Please provide in that ticket as many details as possible about your project.