I know this question has been around for a long time, but there does not seem to be any way to bulk update the list price within a price book.
You can create a product list Excel, with prices and upload it to the CRM. Then you have to manually update the list price, one at a time, we have hundreds of products, and the price changes every 3 months. Of course the ability to update the list price by a fixed percent based on the product price would earn you the cigar.
Can we have at least a view in Zoho sheets to make this task easier, having just paid for the CRM module, I am very disappointed.