Currently, there is no way to achieve this without adding an attribute to your records.
Boosting or burying records (using optional filters) requires a specific value, which rules out a range or any conditional logic.
This article describes why you can't do this and shows an example: https://support.algolia.com/hc/en-us/articles/5851934555025
Is there a workaround?
Sure! You can create an additional attribute on your records which holds a specific value. For example, if you were originally trying to boost t-shirts with price < $20, then you could add an attribute 'cheaper_shirts' with a boolean value to each of these records, then use that attribute in your Rule as it is now a specific value.