Unfortunately this isn't currently possible but this is on the app's TODO list. Do you have any idea of how you would like to export them ? How it would look like ?
So far, I am liking this application although i have been using it for the last 4 days.
So, My ideas are either to have an endpoint where you can GET the exported data as xml or csv, you authenticate using a token generated in the application per client. OR to just to have an export button per budget what exports the whole expenses within the budget as csv file.