We've encountered similar issues before among a couple of other clients. Please do the following:
Go to Tools > Options > Logging and set High level of logging.
After that please reproduce the issue and send us the logs(tools > diagnostic). We'll escalate that ticket to R&D, once we receive that info.

Note that High logging level significantly slows down the software so please make sure you set back Low level after reproducing the problem.

Done !
I hope this would help you.

Best regards.
Gilles

There is actually a workaround for that:
First, please stop the backup service by right-clicking on its icon in the lower-left corner of GUI and selecting "stop service'. Close the software now.

1) Navigate to your settings folder(C:\ProgramData\CloudBerryLab\CloudBerry Backup\ by default)
2) Find Enginesettings.list file
3) Open it with Notepad and find the following parameter:
<CostPriceGB>0.03</CostPriceGB>
You can change it to your liking.
4) After changing this string save the changes, re-launch the software and restart the backup service.

Thanks Matt,
I had to change two settings to enable and configure the feature :
<CostShowEstimation>true</CostShowEstimation>
<CostPriceGB>0.005</CostPriceGB>