I wrote this out for a member so I might as well share it here....
To do a bulk price change in "Behind the Scenes":
1. click on the money bag - right most icon, top row that says "Bulk Edit Prices"
2. click "show all names"
3. then check the top little square to "select all on the page"
4. then check the new box that magically appears and says "Select all XX images on all XX pages.
5. then click the gray bar "Edit checked images simultaneously"
Then you can change the prices and save them for all.
Note: After it saves, there is no indication that anything has happened but you can leave the page and double check.
Also there is no guarantee that your default prices on your newly upload work will have these new prices. You might have to set them manually every time.