There is currently no way to update price list items in bulk. With other records, you can export, make changes, and re-import using either the import tool or migration tool, assuming you have all the proper handles and guids. There is no way to do this however for Price List Items. Every time we make changes to our prices, I have to manually change the price of all products 4 times because we have 4 price lists. This is VERY time consuming and inefficient.