What is common between all of the items in the "group"?
It is possible to use a sql statement to update the price of all items that can be retrieved using some common criteria (all items that are displayed in a category, all items that have a master_category_id of x, all items that have the word blue in the product name or description, etc...)
Then there are bulk import/export product programs that can be used to export a series of product, modify something about it and upload the change(s). This is really only suggested if you plan to do such changes more than once (as in daily, weekly, or even monthly). While powerful, they too require a learning curve that may not be worth dealing with if it's a one time only change.
As always, the more info/description provided on how something is desired to work and what it is doing in relation to that helps identify a solution. In this case, more detail about what "group" is to be affected.
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